Patent Application
20220214610
This application claims priority of EP application 19172160.4 which was filed on May 2, 2019 and which is incorporated herein in its entirety by reference.
The present invention relates to a patterning device.
A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may, for example, project a pattern at a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate.
To project a pattern on a substrate a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features which can be formed on the substrate. A lithographic apparatus, which uses extreme ultraviolet (EUV) radiation, having a wavelength within the range 4-20 nm, for example 6.7 nm or 13.5 nm, may be used to form smaller features on a substrate than a lithographic apparatus which uses, for example, radiation with a wavelength of 193 nm.
The use of standard attenuated phase shift patterning devices in a lithographic apparatus may result in only a relatively small % of the radiation intensity being diffracted into diffraction orders that are within the numerical aperture (NA) of the lithographic apparatus. Due to this, a relatively high % of the radiation is lost and this increases the required dose. Therefore, it may be desired to increase the % of radiation intensity diffracted into orders that are within the NA of the lithographic apparatus.
According to a first aspect of the invention, there is provided a patterning device configured for use in a lithographic apparatus, the lithographic apparatus being configured to use radiation for imaging a pattern at the patterning device via projection optics onto a substrate, the patterning device comprising: a first component for reflecting and/or transmitting the radiation, and a second component covering at least a portion of a surface of the first component and configured to at least partially absorb the radiation incident on the second component, wherein the second component comprises a sidewall, wherein at least one part of the sidewall extends away from the first component at an angle, the angle being with respect to a plane parallel to the surface of the first component, and wherein the angle is less than 85 degrees.
This may have an advantage that more radiation may be diffracted into the numerical aperture (NA) of the lithographic apparatus which may decrease the required dose of radiation. The shape of the second component may reduce an intensity of the radiation diffracted into higher orders as compared to an intensity of the radiation diffracted by a standard patterning device (with sidewalls perpendicular to the corresponding first component). This may improve throughput of the lithographic apparatus.
The second component may at least partially transmit the radiation incident on the second component so as to give the radiation emerging from the second component a phase shift relative to the radiation reflected off another portion of the first component not covered by the second component. The patterning device may be an attenuated phase shift patterning device.
The at least one part of the sidewall may be a substantial part of the sidewall.
The at least one part may be a majority part of the sidewall.
The sidewall may extend away from the first component at the angle at a substantially half way point of the sidewall.
The sidewall may have the angle at the substantially furthest point of the sidewall away from the first component.
At the substantially furthest point of the sidewall away from the first component, the sidewall may have a shape of a curve.
The curve may be a sinusoidal curve. This may have an advantage of providing an increased amount of radiation diffracted into the NA of the system when compared with other curves.
The sidewall may extend away from the first component at the angle over all of the sidewall.
The angle may be less than 70 degrees.
The angle may be 45 degrees.
The second component may have a further sidewall substantially opposite the sidewall of the second component, wherein at least one further part of the further sidewall may extend away from the first component at the angle.
The angle at which the further sidewall extends away from the first component may be different from the angle that the sidewall extends away from the first component.
The second component may have one or more additional sidewalls, wherein at least one additional part of the one or more additional sidewalls may extend away from the first component at the angle.
The angle at which the one or more additional sidewalls may extend away from the first component may be different from the angle that the sidewall extends away from the first component.
The patterning device may be at least one of a reflective patterning device, a transmissive patterning device, a binary patterning device, and an attenuated phase shift patterning device.
Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:
The illumination system IL is configured to condition the EUV radiation beam B before the EUV radiation beam B is incident upon the patterning device MA. Thereto, the illumination system IL may include a facetted field mirror device 10 and a facetted pupil mirror device 11. The faceted field mirror device 10 and faceted pupil mirror device 11 together provide the EUV radiation beam B with a desired cross-sectional shape and a desired intensity distribution. The illumination system IL may include other mirrors or devices in addition to, or instead of, the faceted field mirror device 10 and faceted pupil mirror device 11.
After being thus conditioned, the EUV radiation beam B interacts with the patterning device MA. As a result of this interaction, a patterned EUV radiation beam B′ is generated. The projection system PS is configured to project the patterned EUV radiation beam B′ onto the substrate W. For that purpose, the projection system PS may comprise a plurality of mirrors 13,14 which are configured to project the patterned EUV radiation beam B′ onto the substrate W held by the substrate table WT. The projection system PS may apply a reduction factor to the patterned EUV radiation beam B′, thus forming an image with features that are smaller than corresponding features on the patterning device MA. For example, a reduction factor of 4 or 8 may be applied. Although the projection system PS is illustrated as having only two mirrors 13,14 in
The substrate W may include previously formed patterns. Where this is the case, the lithographic apparatus LA aligns the image, formed by the patterned EUV radiation beam B′, with a pattern previously formed on the substrate W.
A relative vacuum, i.e. a small amount of gas (e.g. hydrogen) at a pressure well below atmospheric pressure, may be provided in the radiation source SO, in the illumination system IL, and/or in the projection system PS.
The radiation source SO may be a laser produced plasma (LPP) source, a discharge produced plasma (DPP) source, a free electron laser (FEL) or any other radiation source that is capable of generating EUV radiation.
Phase shift patterning devices are photomasks that take advantage of the interference generated by phase differences to improve image resolution in photolithography. A phase shift patterning device relies on the fact that radiation passing through a transparent media (i.e. in this case being reflected from that media) will undergo a phase change as a function of its optical thickness.
The attenuated phase shift patterning device MA comprises a first component 22 for reflecting radiation and a second component 24 for reflecting radiation with a different phase with respect to the radiation reflected from the first component. The first component 22 comprises a standard multilayer mirror, e.g. alternating layers of molybdenum and silicon. The layers of the multilayer are not shown in
Although embodiments directed to an attenuated phase shift patterning device are described, it will be appreciated that these embodiments are exemplary and the invention described is also applicable to other types of patterning devices. For example, other patterning devices called “binary masks” may be used. The name “binary” originates from the ideal picture where on the mask either all the radiation is absorbed (zero) or no light is absorbed (one). Patterning devices for EUV radiation may use tantalum as the base material.
The second component 24 is in a different layer from the first component 22, i.e. the second component 24 is located on the first component 22.
The second component 24 reflects a relatively small amount of radiation when compared with the first component 22. The radiation reflected from the second component 24 is not strong enough to create a pattern on the substrate W, but it can interfere with the radiation coming from the first component 22, with the goal of improving the contrast on the substrate W. The contrast may be considered to be the steepness, or sharpness, of the features formed in the image on the substrate W.
As can be seen in
The second component 24 covers the covered portion 22b of the first component 22 which extends a distance d from the uncovered portion 22a of the first component 22. The optimal width will be feature and pitch dependent.
The second component 24 covers at least a portion (the covered portion 22b) of a surface of the first component 22 and is configured to at least partially absorb the radiation incident on the second component 24 and at least partially transmit the radiation incident on the second component 24 so as to give the radiation emerging from the second component 24 a phase shift relative to the radiation reflected off another portion (uncovered portion 22a) of the first component 22 not covered by the second component 24. The second component 24 has a width d which corresponds to the extent in the direction (taken parallel to the surface of the first component 22) of the covered portion 22b of the first component 22. The width d is depicted as a double arrow in
Although only a single uncovered portion 22a is shown in
The terms cover/covered/covering as used within this description is intended to mean that the covering component is in a position such that radiation is at least partially blocked from being incident on the portion of the covered component underneath the covering component. That is, covering may be taken to encompass covering where the covering component is in direct contact with the covered component or not, i.e. another component may or may not be located between the component that is covering and the component being covered.
In this embodiment, the second component 24 comprises the material Ruthenium (Ru) with a thickness t (shown as a double arrow in
The attenuated phase shift patterning device MA may be used in the lithographic apparatus LA by reflecting radiation from the first component 22 of the attenuated phase shift patterning device MA, and reflecting radiation from the second component 24 of the attenuated phase shift patterning device MA. More particularly, reflecting radiation from the pattern comprising the uncovered portion 22a of the first component 22 and generating the patterned radiation beam B′. The effect of this is that the radiation reflected from the second component 24 has a different phase with respect to the radiation reflected from the first component 22 and provides a pattern on the substrate W with increased contrast.
The second component 24 has sidewalls 26a, 26b which are angled with respect to the first component 22. That is, they do not extend wholly perpendicularly to the surface 23 of the first component 22 as in a standard patterning device. The size of the second component 24 in the direction in which the distance d is taken decreases with increasing distance (thickness t) from the first component 22. The second component 24 may be considered to have a rounded corner or a curve at substantially the furthest point of the sidewalls 26a, 26b away from the first component 22. In some embodiments, the sidewalls may be completely curved (i.e. no straight sections) or one or more other parts of the sidewall may be curved.
The second component 24 having the shape as shown in
This will improve throughput of the lithographic apparatus LA (i.e. the number of substrates W that pass through the lithographic apparatus LA in a particular time) when compared to the standard patterning device having a second component made of Ru with straight sidewalls extending perpendicular to the first component. Furthermore, the patterning device MA having the second component 24 will improve throughput and yield (i.e. measure of substrates without defects) when compared to the standard patterning device having a second component made of Ta with straight sidewalls. This is because with more radiation the features may be printed with better quality in the resist on the substrate W.
Table 1 below compares the loss of photons for a standard 60 nm (thickness) Ta-based mask and a 35-nm (thickness) Ru-based attenuated phase shift mask (PSM). The Ru mask has a lower extinction coefficient and a thinner layer. Therefore, less radiation is lost upon a double pass through the mask absorber. The example here is given for dense contact holes (CHs) with 20% mask bias, so that 72% of the mask area is covered by absorber material.
Additionally, a large fraction of radiation is lost, since only the 0th and 1st order are within the NA (numerical aperture) of the system. The second column of table 1 shows the fraction of the radiation intensity that is distributed over orders that are outside the NA. This is larger for the Ru mask than for the Ta mask (more radiation goes into higher orders). 80% of the radiation goes into orders that are outside the NA for the Ru mask and therefore there would be a gain up to a factor 5 if all the radiation was diffracted within the NA. This is more than with the Ta mask where 70% of the radiation goes into orders that are outside the NA.
The amount of radiation diffracted into the −1 order (which may also be outside the NA for off-axis illumination) will never be substantially lower than the amount of radiation in the +1 order and therefore it is theoretically not possible to reduce the amount of radiation into orders outside the NA to 0. In a rough upper limit the amount of radiation in +1, 0, and −1 would be equal and thus 33% of the radiation would be discarded. In the situation with the standard Ru mask, only 20% of the radiation was used (i.e. captured in the NA) whereas using the patterning device MA with the shape of the second component 24 means 67% of the radiation may be available for use. This means that the upper limit would give a dose gain of approximately factor 3 (i.e. 67% of the radiation being available for use is approximately 3×20% previously used). More generally, the patterning device MA provides a substantial gain in dose with respect to a standard patterning device with a second component made of Ru.
It will be appreciated that the described shape of the second component 24 of the patterning device MA may also be used with patterning devices having second components made from materials other than Ru. For example, these may be second components made from Tantalum or other absorbers, such as high k absorbers of e.g. Nickel or Cobalt, and other attenuated phase shift patterning device materials like Rhodium.
The shape of the second component 24 may be formed by isotropic plasma etching (pressure higher), depositing layers on top of discrete chunks of conventionally made absorber material with sharp edges (the sharpness will disappear with the additional layers deposited on top), etch away the material in between the sinusoidal bumps, and/or ion gunning.
The second component 34 (made of Ru) has sidewalls 36a, 36b which are angled with respect to the first component 32 in a similar way as in
The patterning device 30 also provides a gain in dose with respect to a standard patterning device having a second component made of Ru in a similar way as described above with respect to
In some embodiments, the curve of the sidewall at or near the substantially furthest point of the sidewall away from the first component may be a sinusoidal curve. This may provide an increased amount of radiation diffracted into the NA of the system when compared with other curves.
More particularly, the sidewall 56a of the second component 54 extends away from the first component 52 at an angle α, the angle α being with respect to the surface 53 of the first component 52, the angle α being less than 70 degrees. The angle being above 70 degrees may provide relatively little throughput gain. In this embodiment, the sidewall 56a extends away from the first component 52 at the angle α taken with respect to a plane P parallel to the surface 53 of the first component 52, the plane P being at a substantially half way point of the sidewall 56a. It will be appreciated that the plane P may be taken at any point along the sidewall 56a and as can be seen from
The patterning device 50 also provides a gain in dose with respect to a standard patterning device having a second component made of Ru in a similar way as described above with respect to
It will be appreciated that, in other embodiments, the sidewall of the second component may be different, i.e. have a different shape or a different angle with respect to a plane parallel to the surface of the first component over some or all of the length of the sidewall. For example, only a part of the sidewall may have the angle α(e.g. which is less than 70 degrees). In some embodiments, the part of the sidewall extending at the angle α may extend over a substantial part of the sidewall. In some embodiments, the part of the sidewall extending at the angle α may extend over a majority part of the sidewall, i.e. over more than half of the sidewall. The part of the sidewall extending at the angle α may be at or near substantially the furthest point of the sidewall away from the first component.
It will be appreciated that, in other embodiments, the angle α may be less than 85 degrees. In other embodiments, the angle α may be 45 degrees. The optimal angle will depend on the thickness of the second component (which as mentioned may be anywhere between 30 nm and 70 nm) and will also depend on the feature size and pitch (which can also cover a large range of sizes). It will also be appreciated that the sidewall may have different angles at different parts of the sidewall. For example, the sidewall may have a part with a 90 degree angle close to the first component, then have a part with a 45 degree angle (e.g. at a substantially half way point of the sidewall) and then another part further from the first component with a 90 degree angle. As another example, the sidewall may have a part with a 45 degree angle, then have a part with a 90 degree angle, then have a part with a 45 degree angle and so on. Therefore, e.g. the substantial part (or majority part) of the sidewall extending at the angle α(e.g. 45 degrees) need not be continuous and may have sections where the sidewall does not have the angle α.
In some embodiments, the sidewall 56a and the sidewall 56b (i.e. a further sidewall opposite the sidewall 56a) may have the same angle α. More particularly, a further part of the further sidewall may extend away from the first component 52 at the same angle α. However, in other embodiments, the sidewalls 56a, 56b may extend away at different angles.
In some embodiments, the second component 54 may have one or more additional sidewalls (not shown), these sidewalls may form a different part of the second component 54 and/or may extend in perpendicular directions to the sidewalls 56a, 56b of the second component 54. The additional sidewall(s) may have the same angle α or may have a different angle to the sidewall 56a (and the sidewall 56b). More particularly, an additional part of one or more of the additional sidewalls may extend away from the first component 52 at the same angle α or a different angle.
Although the above description has been concerned with a reflective phase shift patterning device (i.e. for use with EUV radiation), the structure of the second component described above may also be used in a transmissive patterning device (such as for use with DUV radiation). For example, in this case, the first component may be transmissive. The transmissive patterning device may be a binary patterning device.
Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin-film magnetic heads, etc.
Although specific reference may be made in this text to embodiments of the invention in the context of a lithographic apparatus, embodiments of the invention may be used in other apparatus. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes an object such as a wafer (or other substrate) or mask (or other patterning device). These apparatus may be generally referred to as lithographic tools. Such a lithographic tool may use vacuum conditions or ambient (non-vacuum) conditions.
Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention, where the context allows, is not limited to optical lithography and may be used in other applications, for example imprint lithography.
Where the context allows, embodiments of the invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read only memory (ROM); random access memory (RAM); magnetic storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other forms of propagated signals (e.g. carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions in fact result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc. and in doing that may cause actuators or other devices to interact with the physical world.
While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.
| Number | Date | Country | Kind |
|---|---|---|---|
| 19172160.4 | May 2019 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2020/059366 | 4/2/2020 | WO | 00 |
