Patent Application
20140168623
1. Field of the Invention
The present invention relates to an exposure apparatus, an exposure method, and a method of manufacturing a device.
2. Description of the Related Art
A projection optical system of an exposure apparatus is required to have extremely excellent optical performance. Hence, various adjustment mechanisms of optical performances such as a magnification adjustment mechanism and a wavefront aberration adjustment mechanism have been added to the projection optical system so far. Adjustment of a rotationally asymmetric aberration, which remains in the projection optical system or occurs when using it, is also a problem. There are various types of rotationally asymmetric aberration, and a rotationally asymmetric aberration having twofold symmetry in particular tends to remain or occur in the projection optical system. Twofold symmetry refers to the property of overlapping an original pattern after a half rotation. Representative rotationally asymmetric aberrations having twofold symmetry are astigmatism, and a difference between longitudinal and lateral magnifications. In the case of the astigmatism, when a pupil coordinate of the projection optical system is represented as (r, θ) on a polar coordinate system, the wavefront aberration is represented in the form of r̂2×cos(2θ+φ) and has twofold symmetry with respect to the pupil coordinate.
In addition, in the case of C2Mag, a distortion (image shift) has twofold symmetry with respect to an image plane coordinate. Note that although the term “C2Mag” is used in this specification, this term means not only the magnification difference between the longitudinal direction and the lateral but also the magnification difference between two arbitrary, orthogonal directions.
In other words, C2mag is defined as anisotropic magnification having 2-fold rotational symmetry.
Furthermore, regarding the astigmatism, and C2mag, higher order (the order is high in the radial vector direction) aberrations may occur.
These astigmatism and difference between longitudinal and lateral magnifications may occur as a result of errors in the plane of a lens or a mirror which constitutes the projection optical system, and a residual error which cannot be adjusted completely upon assembly may remain in the projection optical system. The astigmatism and C2mag may also occur when the projection optical system absorbs exposure heat and warms up asymmetrically with respect to its optical axis. In this case, these aberrations continue to change in accordance with the absorbed exposure heat amount.
As a characteristic of an aberration having twofold symmetry, there are two types of fundamental aberration components, and an aberration in every direction can be represented by their linear combination. For example, when the wavefront aberration is astigmatism (AS), it has two fundamental components: ASc=r̂2×cos(2θ) and ASs=r̂2×sin(2θ), and the astigmatism AS in every direction can be represented as a linear combination of these components: AS=C1×ASc+C2×ASs.
On the other hand, in the case of C2mag, C2mag can be represented by a linear combination of two fundamental aberrations, that is, C2Mag in a 0° direction and that in a 45° direction. First of all, C2mag can be represented as:
dx=(M/2)(x cos 2θ+y sin 2θ)
dy=(M/2)(x sin 2θ−y cos 2θ) (1)
where dx represents the image shift amount in the X direction, dy represents the image shift amount in the Y direction, M represents the magnitude, and θ represents the direction.
When θ=0°, equation (1) is rewritten as equation (2) below. This case will be referred to as TY—0 hereinafter (see
dx=(M/2)x
dy=−(M/2)y (2)
Furthermore, when θ=45°, equation (1) is rewritten as to equation (3) below. This case will be referred to as TY—45 hereinafter (see
dx=(M/2)y
dy=(M/2)x (3)
By using these two components, TY—0 and TY—45, C2mag in every direction can also be represented by a linear combination of two performances of TY—0 and TY—45 for arbitrary θ in equation (1).
According to Japanese Patent No. 03341269, the rotationally asymmetric optical performance having twofold symmetry at a particular direction of the projection optical system is conventionally adjusted by providing two members with rotationally asymmetric shapes and changing the gap between the two members or relatively rotating the two members. Conventionally, the adjustment of an aberration component having twofold symmetry has been used for the purpose of compensating for an asymmetric expansion of a reticle in a projection optical system, or adapting to the deformation of an underlayer which has already been exposed in a step-and-scan exposure apparatus (a distortion, which is called a skew component and turns into a parallelogram is known to occur in a step-and-scan exposure apparatus). In those cases, only the TY—0 component need be controlled in the former, and only the TY—45 component need be controlled in the latter. Hence, an effect can be obtained to a certain degree as long as the projection optical system is equipped with a mechanism for controlling only the TY—0 component or the TY—45 component.
However, as the requirement for overlay accuracy increases, there is an increasing demand for controlling both the TY—0 component and the TY—45 component. Particularly in recent years, the exposure apparatus has been required to perform exposure in accordance with a distorted shot within a distorted wafer along with the proliferation of a chip laminating technique such as TSV (Through-silicon via) or a back-side illumination CMOS sensor. Note that TSV is a mounting technology using a silicon feedthrough electrode. Distortion of the wafer is not a unique phenomenon and has a different magnitude and direction for each location. Therefore, in order to adapt to the distortion of the wafer, the exposure needs to be performed with changing the magnitude and the direction of C2mag of the projection optical system for each shot. In order to achieve this, the projection optical system needs to mount a mechanism, which is capable of controlling both the TY—0 component and the TY—45 component.
In a method described in Japanese Patent No. 03341269, it was required to position two units for controlling C2mag in one direction to form an angle of 45° each other or to make the entire unit for controlling C2mag in one direction rotatable in order to control both the TY—0 component and the TY—45 component. However, positioning two units for controlling C2mag in one direction to form an angle of 45° is difficult in terms of space. In general, because the projection optical system is required to have extremely high optical performance, lenses are densely packed from the object plane to the image plane without any gaps to correct aberrations, and lens barrel components for holding them are arranged without any gaps. Securing a space for positioning both a rotationally asymmetric member and a mechanism for precisely controlling it in the optical path of a projection optical system may be possible if only for one set, but is difficult for two or more sets in terms of design.
Furthermore, it is also difficult to make the entire unit for controlling C2mag in one direction rotatable in terms of driving accuracy. In the case of a mechanism for controlling C2mag by changing the gap between the two members, the gap between the two members is changed very precisely so as not to change anything other than the gap (such as movement or a tilt in a direction perpendicular to the optical axis or the like) in order not to influence other optical performances. Hence, the range of the change (stroke) in the gap between the two members is naturally limited to the range between several hundreds μm and several mm. The same goes for a mechanism for controlling C2mag by rotating the members, and the stroke of a rotation angle is limited from several minutes to several degrees. However, when rotating the entire unit in order to control the direction in which C2mag occurs, that range must cover every direction in 360 degrees. Rotating the unit in such a broad range freely as well as precisely without any axis shift or tilt is extremely difficult because of its mechanical structure. Moreover, the need for driving between the shots at a high speed makes it even more difficult.
Furthermore, whereas a method of correcting two different aberrations using the drive of one member has been examined, a method of correcting independent components of one aberration in an arbitrary direction by driving one member has not been examined.
The present invention provides an exposure apparatus which controls one aberration having twofold symmetry with regard to an arbitrary direction by driving one member.
The present invention in its one aspect provides an exposure apparatus of projecting a pattern of a reticle on a substrate via a projection optical system and exposing the substrate to light, the apparatus comprising: an optical element positioned along an optical axis of the projection optical system and configured to include a surface having a rotationally asymmetric shape; a driving unit configured to drive the optical element with at least two degrees of freedom; and a control unit configured to control the drive with two degrees of freedom to correct an aberration having twofold symmetry in a direction represented by a linear sum of the aberration of components in two directions based on information showing a relationship between a driving amount with two degrees of freedom and the components of the aberration in the two directions, and an amount to be adjusted of each of the components of the aberration in the two directions.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Note that the present invention is not limited to the following embodiments, which are merely concrete examples advantageous for practice of the present invention. In addition, not all combinations of features described in the following embodiments are essential for the solution to the problem in the present invention.
The shape of an aperture portion of an aperture stop 105 in the illumination optical system 104 is almost circular, and an illumination optical system control unit 108 can set the diameter of its aperture portion and the numerical aperture (NA) of the illumination optical system 104 to desired values. In this case, since the value of the ratio of the numerical aperture of the illumination optical system 104 of that of a projection optical system 110 is a coherence factor (σ value), the illumination optical control unit 108 can set the σ value by controlling the aperture stop 105 of the illumination optical system 104.
A half mirror 106 is positioned in the optical path of the illumination optical system 104, and a part of the exposure light for illuminating the reticle 109 is reflected and extracted by this half mirror 106. An ultraviolet photosensor 107 is positioned in the optical path of the reflected light by the half mirror 106 and generates an output corresponding to the intensity (the exposure energy) of the exposure light. The pattern on a circuit of a semiconductor device to be printed is formed on the reticle (mask) 109 as an original and illuminated by the illumination optical system 104. The projection optical system 110 reduces the pattern on the reticle 109 to a reduction magnification β (for example, β=½), and is positioned to project one shot region on a wafer (substrate) 115 on which a photoresist is coated. The projection optical system 110 can be an optical system of a refractive type, a catadioptric system, or the like.
An aperture stop 111 whose aperture portion is almost circular is positioned on the pupil plane (a Fourier transform plane for the reticle) of the projection optical system 110, and the diameter of the aperture portion can be controlled by an aperture stop driving unit 112 such as a motor. An optical element driving unit 113 moves an optical element, which constitutes a part of a lens system in the projection optical system 110 such as a field lens, along the optical axis of the projection optical system 110. This keeps the projection magnification at a satisfactory value to reduce a distortion error while preventing various aberrations of the projection optical system 110 from deteriorating. A projection optical system control unit 114 controls the aperture stop driving unit 112 and the optical element driving unit 113 under the control of a main control unit 103.
A wafer stage (substrate stage) 116 for holding a wafer 115 is movable in three-dimensional directions, and can move in the direction of the optical axis (the Z direction) of the projection optical system 110 and within a plane (X-Y plane) perpendicular to the direction of the optical axis. Note that in
A projection optical system 121 and a detection optical system 122 detect a focal plane. The light projection optical system 121 projects a plurality of light beams formed by non-exposure light to which the photoresist on the substrate 115 is not sensitive, and each light beam is focused on and reflected by the wafer 115. The light beam reflected by the wafer 115 is incident on the detection optical system 122. Although illustration is omitted, a plurality of light-receiving elements for position detection are positioned in correspondence with the respective reflected light beams within the detection optical system 122, and the detection optical system 122 is configured so that the light-receiving surface of each position detection light-receiving element is nearly conjugate with the reflection point of each light beam on the wafer 115 by an imaging optical system. The positional shift of the surface of the wafer 115 in the optical axis direction of the projection optical system 110 is measured as that of light incident on the light-receiving elements for position detection within the detection optical system 122.
As shown in
The configuration of the aberration adjustment member 21 in
z=Ax
3
+B(x+y)3 (4)
where A and B are constants.
The rotationally asymmetric shape represented by equation (4) is a shape shown in
The distortion of the TY—0 component shown in
Moreover, the surface of the aberration adjustment member 21 with a rotationally asymmetric shape has may, for example, be a shape represented by:
z=Ar
3 cos 3θ or
z=Br3 sin 3θ (5)
where r and θ are variables, and A and B are constants.
In this case, the two directions in which the optical element 211 is driven are set to be two directions of the X-axis direction and the Y-axis direction. Therefore, by driving the one optical element 211 in an arbitrary direction on the plane defined by the X-axis direction and the Y-axis direction, C2mag can be controlled with regard to an arbitrary direction.
An example of an exposure method using the aberration adjustment member 21 for adjusting an aberration having twofold symmetry will now be described with reference to
In step S2, the main control unit 103 calculates an amount to be adjusted (adjustment amount) of the components (the TY—0 component and the TY—45 component) of the aberration in the two directions for exposure in accordance with the shape of each shot region. The main control unit 103 may also calculate the adjustment amounts of other image shift components. In step S3, the optical element control unit 123 obtains the driving amount with two degrees of freedom based on the information showing the relationship between the driving amount with two degrees of freedom and the components of the aberration in the two directions, and the adjustment amounts of the components of the aberration in the two directions. The optical element control unit 123 drives the optical element 211 by the optical element driving unit 22 to adjust the TY—0 component and the TY—45 component based on the obtained driving amount with two degrees of freedom. At this time, in order to further adjust other image shift components, simultaneous driving may be performed for the optical element of the projection optical system 110 by the optical element driving unit 113 via the projection optical system control unit 114 and the wafer stage 116 by the stage driving unit 119 via the stage control unit 120. Upon completion of driving the optical element 211, the main control unit 103 performs an exposure in step S4.
In step S5, the main control unit 103 drives the wafer stage 116 so as to move the shot to be exposed next. The main control unit 103 continues to drive the optical element 211 and to perform exposure based on the results of the measurement of the distortion of the shot regions and the calculation of the adjustment amount executed in advance in steps S1 and S2. After completion of exposing all shot regions is confirmed in step S6, the main control unit 103 unloads the wafer, and then loads a next wafer to repeat the flow shown in
In the exposure method based on this flow, the exposure can be performed in accordance with a shot shape adapted to a shot distortion to be the underlayer by correcting C2mag having twofold symmetry with regard to an arbitrary direction, and thus overlay accuracy increases.
The aberration adjustment member 21 in Example 2 for adjusting an aberration having twofold symmetry will be described with reference to
The distortion of the TY—0 component shown in
Hence, a difference between longitudinal and lateral magnifications can be created and controlled with regard to an arbitrary direction by rotational driving of the optical element 211 in an arbitrary direction about the intersection of the plane with the wedge and the Z-axis. It is also possible to use this aberration adjustment member 21 to control the rotationally asymmetric difference between longitudinal and lateral magnifications having twofold symmetry with regard to an arbitrary direction, and perform exposure in the same manner as in Example 1.
The aberration adjustment member 21 in Example 3 for adjusting the aberration having twofold symmetry will be described with reference to
The distortion of the TY—0 component shown in
As explained above, the main control unit 103 in Examples 1 to 3 controls a direction of an aberration having twofold symmetry determined in accordance with a position in two degrees of freedom of the optical element having different powers in two directions by using the optical element driving unit 113 which drives the optical element with at least two degrees of freedom.
As in the first embodiment, an astigmatism (AS) can be created and controlled with regard to an arbitrary direction by combining a drive of the optical element 211 with two degrees of freedom.
A method of manufacturing a device (for example, a semiconductor device or a liquid crystal display device) according to the first embodiment of the present invention will now be described. A semiconductor device is manufactured by a preprocess of forming an integrated circuit on a wafer, and a post-process of completing, as a product, a chip of the integrated circuit formed on the wafer by the preprocess. The preprocess includes a step of performing a scan exposure for the wafer coated with a photosensitive agent using the above-described exposure apparatus, and a step of developing the wafer. The post-process includes an assembly step (dicing and bonding) and packaging step (encapsulation). A liquid crystal display device is manufactured by a step of forming a transparent electrode. The step of forming a transparent electrode includes a step of coating with a photosensitive agent a glass substrate on which a transparent conductive film is deposited, a step of performing a scan exposure for the glass substrate coated with the photosensitive agent using the above-described exposure apparatus, and a step of developing the glass substrate. The device manufacturing method according to the embodiment can manufacture higher-quality device than the prior arts.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2012-276121, filed Dec. 18, 2012, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-276121 | Dec 2012 | JP | national |
