DE102017114504B4 - lithography exposure device - Google Patents

Abstract

Lithography exposure device with an exposure unit (5) comprising an imaging matrix (2) with a large number of pixels (P) and a telecentric lens (1) with an optical axis (A), and a workbench (4) with a support surface (4.1) for the relative Arrangement and relative movement of a substrate with a photoresist layer (3) to the lens (1) in a movement direction (R), the telecentric lens (1) having a first lens group (L1) with a first image-side focal plane (BE1') and a second lens group (L2) with a second object-side focal plane (BE2), and the first image-side focal plane (BE1') and the second object-side focal plane (BE2) coincide in a pupil plane (PE), in which an aperture stop (AP) is arranged, with an aperture that results in an object-side opening angle (αO) of the lens (1), which is adapted to a beam angle (αP) of the pixels (P) and that results from the object-side opening angle (αO) and a reproduction scale of the lens (1) resulting image-side opening angle (αB) is greater than is required for a required resolution of image pixels (BP) exposed by the imaging of the pixels (P), and from which a calculated Length (IR) for a depth of field (T), characterized in that the imaging matrix (2) is imaged in an image plane (BB) which is tilted to a plane (E) defined by the bearing surface (4.1) or an actual length (IT) of the depth of field (T) is at least 1.5 times greater than the calculated length (IR) resulting from the opening angle (αB) on the image side.

Description

A lithography exposure apparatus includes an exposure unit and a work table, wherein the exposure unit can be moved relative to the work table in a predetermined travel direction in order to stepwise multiply expose a photoresist layer arranged on the work table. The yield in photolithography is proportional to the light energy introduced into a photoresist layer of a substrate (e.g. wafer or screen carrier) per pixel during the total exposure time. In the case of maskless photolithography, individual pixels of an imaging matrix are usually imaged in each case as an image pixel on the photoresist layer via an exposure lens. The image generator matrix and the exposure lens, which together form an exposure unit, are moved relative to the photoresist layer of the substrate, which lies on a workbench, in a direction of travel equal to a longitudinal extension of the image generator matrix, so that each image pixel can be exposed step by step as often as the Image generator matrix has pixels in the longitudinal dimension in question. The more pixels the imaging matrix has in the direction of travel, the more frequently an image pixel is exposed and the more light energy is introduced into an image pixel. Consequently, large amounts of light energy can be entered using multiple imager matrices. A parallel use, in which a simultaneous exposure of one image pixel each by one pixel of the imager matrices, is structurally difficult. A sequential use, in which the image pixels are exposed sequentially by the pixels of the individual imager matrices, is more time-consuming. Both variants make the exposure unit comparatively more complex and expensive.

In parallel or alternatively, the lens is designed in such a way that the light output emitted by each pixel of the imaging matrix is transferred as completely as possible to each image pixel. The light intensity that is reflected by a secondary emitter, such as a micromirror array (DMD), should also be understood as the emitted light output, which is correctly only spoken of in the case of primary emitters.

As a rule, a telecentric lens is used as the exposure lens, the optical scheme of which is in 1 is used, which images an image generator matrix 2 positioned in the object-side focal plane BE ₁ of a first lens group L ₁ into the image-side focal plane BE ₂ ′ of a second lens group L ₂ in which a substrate with a photoresist layer is arranged. The aperture stop AP is in the pupil plane PE of the lens, which coincides with the image-side focal plane BE ₁ ' of the first lens group and the object-side focal plane BE ₂ of the second lens group L ₂ and thus determines the object-side and image-side opening angle α _O via the size of its opening , α _B , from which the object-side and image-side numerical aperture of the lens 1 result.

In contrast to photolithographic exposure with masks, in which the object structure to be imaged can be of any size and can therefore be kept very small, so that it is imaged on the photoresist layer with a standardized imaging scale of 0.25x, the object structure is transparent when exposed with an imaging matrix the size of the pixels has a lower limit. The image structures to be imaged on the photoresist layer are generally not significantly larger than a pixel, so that the imaging scale, determined by the focal length ratio f ₂ /f ₁ , is less than 1.5.

The light conductance, determined by the given pixel size and the given beam angle α _P of the pixels of the imaging matrix, remains constant over the beam path through the lens 1, which is why, with a magnification of, for example, 1:1, an image-side opening angle α _B is equal to the object-side opening angle α _O results. Accordingly, the image-side numerical aperture is, on the one hand, larger than is necessary for a required resolution, and, on the other hand, this results in only a small depth of field. The surface flatness of a photoresist layer to be exposed is often subject to a greater tolerance than the depth of field is large, so that at least some of the pixels P are not imaged sharply on the photoresist layer. This means that the light output transmitted by the lens is only fully introduced into the image pixels that lie within the depth of field.

This means that high demands must be placed on the evenness of the photoresist layer so that it lies within the small depth of field over the entire extent of the substrate, which can hardly be met in practice. Alternatively, enabling focus tracking so that the photoresist layer is always in the depth of field during exposure is very complex in terms of equipment and control technology and is only feasible if the change in distance to the lens has a flat increase, so that the change in distance over the longitudinal extent of the imaging matrix in the direction of travel is only slight is.

The depth of field can be increased by tilting a reticle/object plane and/or a wafer/image plane.

To this end, the U.S. 5,194,893A disclose an exposure method and a projection exposure apparatus for projecting a pattern formed in a transfer area on a mask onto an exposure area to be exposed on a photosensitive substrate with a view to improving a depth of field. The projection exposure device includes a projection system, a mask table for the one-dimensional movement of the mask, and a substrate table for the one-dimensional movement of a substrate. The projection exposure apparatus further comprises a substrate holder, which is designed to hold the photosensitive substrate on the substrate table at a predetermined inclination angle with respect to the direction of the one-dimensional movement, driving means for the substrate holder for moving the substrate holder along an optical axis of the projection system, and control means for controlling the drive means.

From the U.S. 6,673,526 B1 a method and an apparatus for producing a pattern on a substrate are known. The device includes a phase-shifting mask having a pattern and a light source for irradiating the mask with light to transfer the pattern of the mask onto a substrate. A depth of field is increased in that a reticle plane, in which the phase-shifting mask is located, can be tilted with respect to the light coming from the light source.

The depth of focus can also be improved by using a spectrally broadband or tunable light source through the dispersion-related focus shift of the imaging optics.

To this end, the U.S. 2007/0013889 A1 a lithographic apparatus comprising an illumination system emitting a beam having two beam components whose frequencies differ, an array of individually controllable elements structuring the beam, and a substrate table supporting a substrate. The lithography apparatus further includes a projection system that projects the structured beam onto a target portion of the substrate, the projection system focusing the first and second beam components at different heights with respect to the substrate table to increase a depth of field.

A device for aligning a projection for projecting a mask pattern onto a substrate and an exposure method are from U.S.A. 4,937,619 known. The device comprises means for emitting a plurality of light beams with different wavelengths and projection exposure means for focusing the mask pattern on different positions along an optical axis depending on the wavelength of the respective light beam. By focusing the mask pattern in different positions along the optical axis, a depth of field is increased.

In order to increase the depth of field, it is common practice to adjust the opening of the aperture stop in such a way that there is a smaller numerical aperture on the image side, which still leads to sufficient resolution and a larger depth of field for a given wavelength of the light to be imaged.

However, this also inevitably reduces the object-side aperture, so that the light output emitted by each pixel is no longer fully coupled into the lens. In order to finally introduce the same light energy into an image pixel with a lower light output, only the respective exposure duration and/or the number of exposures per image pixel can then be increased. The former leads to an increased process duration, the latter leads to a higher expenditure on equipment.

The object of the invention is to create a lithography exposure device with which the entry of the light output emitted by one of the pixels of an imaging matrix into an image pixel on a photoresist layer is increased, which lies outside a depth of field range calculated from the image-side aperture.

This object is achieved for a lithography exposure device according to claim 1. Advantageous versions are specified in subclaims 2 to 5.

The invention will be explained in more detail below using exemplary embodiments and drawings.

• 1 ein Optikschema eines telezentrischen Objektivs, wie es identisch oder in modifizierter Form in einer erfindungsgemäßen Lithographiebelichtungsvorrichtung verwendet wird und zur Erläuterung der Aufgabenstellung dient,
• 2 ein erstes Ausführungsbeispiel einer Lithographiebelichtungsvorrichtung mit einem Objektiv gemäß 1 und einer hierzu verkippten Bildgebermatrix,
• 3 ein zweites Ausführungsbeispiel mit einer zur Auflagefläche eines Werktisches verkippten Belichtungseinheit, enthaltend ein Objektiv gemäß 1 und
• 4 ein drittes Ausführungsbeispiel bei dem das Objektiv, modifiziert zu einem Objektiv nach 1, als ein verstimmter Achromat ausgeführt ist.

For this show:

• 1 an optical scheme of a telecentric lens, as used identically or in a modified form in a lithography exposure device according to the invention and used to explain the task,
• 2 a first exemplary embodiment of a lithography exposure device with a lens according to FIG 1 and an image generator matrix tilted to this,
• 3 a second embodiment with an exposure unit tilted to the bearing surface of a work table, containing a lens according to FIG 1 and
• 4 a third embodiment in which the lens modified to a lens after 1 , designed as a detuned achromat.

A first embodiment of a lithography device according to the invention, as in 2 shown, has a workbench 4 and an exposure unit 5 with a telecentric lens 1 and an imaging matrix 2 in the same way as the prior art.
The telecentric lens 1 contains a first lens group L ₁ with a first focal length f ₁ (a distinction between object-side and image-side focal length should be omitted for simplicity), a first object-side focal plane BE ₁ and a first image-side focal plane BE ₁ ', and a second Lens group L ₂ , with a second focal length f ₂ , a second object-side focal plane BE ₂ and a second image-side focal plane BE ₂ '.
The first image-side focal plane BE ₁ 'and the second object-side BE ₂ coincide and form a common pupil plane PE, in which an aperture stop AP is arranged. The size of the diaphragm opening of the aperture diaphragm AP is selected in such a way that an object-side opening angle α _O which is adapted to the radiation angle α _P of the pixels P results. From the object-side aperture angle α _O and the image scale f ₂ /f ₁ of the lens 1, there results an image-side aperture angle α _B , from which, with knowledge of the wavelength of the light emitted by the pixels P, a calculated length I _R for a depth of field T results. The opening angle α _B on the image side is greater than is necessary for the resolution of the image pixels BP resulting from the imaging.

The workbench 4 has a support surface 4.1, which defines a plane E and is used for positioning a substrate and thus a photoresist layer 3 to be exposed relative to the lens 1, for the purpose of carrying out the exposure process. During the exposure, the workbench 4 and the exposure unit 5 are moved relative to one another in such a way that each image pixel BP of a pattern to be exposed onto the photoresist layer 3 is exposed multiple times. The image pixels BP are each successively charged with the light output of the pixels P arranged next to one another in the direction of travel R.

The fact of multiple exposure by pixels P arranged next to one another in the travel direction R enables the object according to the invention to be solved in a first way, in which the imaging matrix 2 is imaged in an image plane BB, which is tilted relative to a plane E defined by the bearing surface 4.1. As a result, the image pixels BP are at least temporarily within the depth of field T around the image plane BB while they are being scanned by the pixels P of a row of pixels P of the imaging matrix 2 arranged in the direction of travel R, even if they differ from the plane with a greater tolerance E differ when the calculated length I _R of the depth of field T is large. In this way, it is possible to introduce more light power in individual exposures into image pixels BP that otherwise lie outside the depth of field T.

In order to image the imaging matrix 2 in an image plane BB, which, in contrast to the prior art, is tilted relative to a plane E defined by the bearing surface 4.1, as in 2 shown, the imaging matrix 2 is arranged on the optical axis A, intersecting the first object-side focal plane BE ₁ and enclosing a first tilt angle β with it, the first tilt angle β and the direction of travel R lying in one plane (drawing plane). Consequently, the pixels P are imaged in an image plane BB that is tilted to the image-side focal plane BE ₂ ′. In this case, the plane E defined by the bearing surface 4.1 is aligned parallel to the second focal plane BE ₂ ′ on the image side.

Alternatively, in a second exemplary embodiment, as in FIG 3 shown, arranged in the object-side focal plane BE ₁ and the optical axis A of the lens 1 encloses an angle γ of less than 90° with the plane E defined by the bearing surface 4.1. Consequently, the pixels P are imaged in an image plane BB which coincides with the image-side focal plane BE _{2 ′} and which is tilted with respect to the plane E.

The two aforementioned exemplary embodiments are practically easy to implement. They do not require any modification of lenses that have already been calculated, but can be used with an object-side opening angle α _O adapted to the beam angle α _P of the pixels P of an imaging matrix 2 and thus an adapted numerical aperture despite a small depth of field T to fulfill the task according to the invention.

The solution of the invention is achieved in a second way, in which the telecentric lens 1 is modified so that the beam guidance of different beam bundle components within the lens 1 is changed either as a function of the wavelength or as a function of the angle in the geometric beam guidance so that an actual length for the lens 1 I _T of the depth of field T results as a superimposition of the depths of field of the various beam components, which is greater than the calculated length I _R resulting from the opening angle α _B on the image side.

This second way of solving the problem is explained on the basis of the following exemplary embodiments.

In contrast to poorly corrected lenses, specific measures are taken here that either stretch the calculated depth of field in a targeted manner in the axial direction or create several foci that are offset axially with respect to one another and thus create depths of field without the resolving power (in the transverse direction) deteriorating below the required resolving power .

A third embodiment, shown in 4 , relates to an embodiment with which different focus positions are created in the axial direction in a wavelength-specific manner.
The lens 1 is usually corrected as an achromat for two wavelengths λ ₁ , λ ₂ of the transmitted light, which means that these two wavelengths λ ₁ , λ ₂ are imaged in the same image-side focal plane, here the second image-side focal plane BE ₂ ′. In order to obtain an actual length I _T of the depth of field T that is greater than the length I _R of the depth of field T ₁ , T ₂ calculated by calculation from the opening angle α _B on the image side for one of the two wavelengths λ ₁ , λ ₂ , the lens 1 calculated in such a way that for the two wavelengths λ ₁ , λ ₂ there are different second focal planes BE ₂ 'λ ₁ , BE ₂ 'λ ₂ on the image side, which are axially offset to such an extent that two partial depths of focus T ₁ , T ₂ result, which either partially overlap axially or abut one another. The actual length I _T of the depth of field T of the lens 1, which is formed by the two partial depths of field T ₁ , T ₂ , increases as a result up to a doubling. Strictly speaking, the use of broadband light means that the edge areas of the wavelength distribution may also be shifted by more than the monochromatic depth of field, because for every wavelength in between, another wavelength can be found, so that their two monochromatic depths of field T ₁ , T ₂ overlap. This results in a closed overlap area. The possible shift is limited by the increasing loss of resolution and contrast as well as by the limited spectral sensitivity of the photoresist. In a practical sense, the polychromatic depth of field T can be enlarged by a factor of 4 compared to the monochromatic depth of field T ₁ , T ₂ .

A fourth exemplary embodiment, not shown in the drawings, relates to an embodiment with which different focus positions are created in the axial direction by influencing the beam bundle components geometrically-optically or wave-optically. In addition to the introduction of a defined amount of spherical aberrations of a maximum of three lambda by targeted detuning of the lens, it is also possible to introduce a special filter in the pupil plane. The mode of action when spherical aberration is introduced is based on the fact that different aperture angle ranges of the bundle in the image space have different focal lengths and thus cause longitudinal errors.
Apart from continuous phase shifts, discrete phase steps are also conceivable. In addition to spherical aberrations as an example of continuous phase shifts, there are also possibilities, in particular through discrete steps, of no longer interfering with beam components and allowing them to form separate larger depths of field that correspond to their respective smaller numerical apertures. In the image plane, these larger depths of field are superimposed to form a larger common depth of field.

Reference List

1

lens

2

imager matrix

3

photoresist layer

4

workbench

4.1

bearing surface

5

exposure unit

L1

first lens group

BE1

object-side focal plane of the first lens group L ₁

BE1'

image-side focal plane of the first lens group L ₁

f1

first focal length

L2

second lens group

BE2

object-side focal plane of the second lens group L ₂

BE2'

image-side focal plane of the second lens group L ₂

f2

second focal length

αP

Beam angle of a pixel P

αO

Object-side opening angle

αB

image-side opening angle

β

first tilt angle between imaging matrix 2 and object-side focal plane BE ₁

g

second tilt angle between optical axis A and plane E

T

depth of field

T1, T2,....Tn

partial depth of field

IR

calculated length of the depth of field T

IT

actual length of depth of field T

A

optical axis

bb

picture plane

P

pixels (of the imager matrix 2)

bp

image pixels

E

level

AP

aperture stop

PE

pupil level

R

travel direction

Claims (5)

Lithography exposure device with an exposure unit (5) comprising an imaging matrix (2) with a large number of pixels (P) and a telecentric lens (1) with an optical axis (A), and a workbench (4) with a support surface (4.1) for the relative Arrangement and relative movement of a substrate with a photoresist layer (3) to the lens (1) in a movement direction (R), the telecentric lens (1) having a first lens group (L ₁ ) with a first image-side focal plane (BE ₁ ') and a second lens group (L ₂ ) with a second object-side focal plane (BE ₂ ), and the first image-side focal plane (BE ₁ ') and the second object-side focal plane (BE ₂ ) coincide in a pupil plane (PE) in which an aperture stop ( AP) is arranged, with an aperture that results in an object-side aperture angle (α _O ) of the lens (1), which is adapted to a beam angle (α _P ) of the pixels (P) and which results from the object lateral opening angle (α _O ) and an imaging scale of the lens (1) resulting image-side opening angle (α _B ) is greater than is required for a required resolution of image pixels (BP) exposed by the imaging of the pixels (P), and from the a calculated length (I _R ) for a depth of field (T) results, characterized in that the imaging matrix (2) is imaged in an image plane (BB) which is tilted relative to a plane (E) defined by the bearing surface (4.1). or an actual length (I _T ) of the depth of field (T) is at least 1.5 times greater than the calculated length (I _R ) resulting from the opening angle (α _B ) on the image side. Lithography exposure device claim 1 , characterized in that the imaging matrix (2) is arranged on the optical axis (A) intersecting a first object-side focal plane (BE ₁ ) and enclosing a first tilt angle (β) therewith, the first tilt angle (β) and the direction of travel ( R) lie in one plane, so that the pixels (P) are imaged in the image plane (BB) tilted to a second image-side focal plane (BE ₂ ') of the lens (1) and the plane (E) defined by the contact surface (4.1) is aligned parallel to the second image-side focal plane (BE ₂ '). Lithography exposure device claim 2 characterized in that the imaging matrix (2) is arranged in the first object-side focal plane (BE ₁ ) and the optical axis (A) of the lens (1) has a second tilting angle (γ) of less than 90° with that defined by the supporting surface (4.1). plane (E), wherein the second tilt angle (g) and the direction of travel (R) lie in one plane, so that the pixels (P) are imaged in the image plane (BB) coinciding with the second image-side focal plane (BE ₂ '), which is tilted with respect to the plane (E). Lithography exposure device claim 1 , characterized in that the lens (1) causes different beam guidance for beam portions of different wavelengths, so that the actual length (I _T ) of the depth of field (T) as a superimposition of the depths of focus of the beam portions is greater than that resulting from the image-side opening angle (α _B ) resulting calculated length (I _R ). Lithography exposure device claim 1 , characterized in that the lens (1) causes different beam guidance for beam portions of different aperture angle ranges, so that the actual length (I _T ) of the depth of field (T) as a superimposition of the depths of focus of the beam portions is greater than that resulting from the image-side opening angle (α _B ) resulting calculated length (I _R ).

Images