Radiation sensor

Abstract

A radiation sensor for detecting EUV radiation, the radiation sensor comprising: a radiation receiving side for receiving radiation to be detected; a substrate layer comprising a photodiode at the radiation receiving side; a cathode configured to collect charge from the photodiode; and a side shield configured to shield the photodiode from radiation entering the substrate layer from an opposite side of the side shield, wherein the side shield extends into the substrate layer from the radiation receiving side.

Description

RADIATION SENSORCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of EP application 23214138.2 which was filed on 5 December 2023 and which is incorporated herein in its entirety by reference.FIELD

[0002] The present invention relates to a radiation sensor for detecting EUV radiation, a stage, an EUV lithographic apparatus and a method for manufacturing a radiation sensor.BACKGROUND

[0003] 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.

[0004] 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.

[0005] It is desirable to know the dose of EUV radiation that is being used. A radiation sensor can be used to detect radiation from a beam of radiation. However, radiation apart from the beam can also contribute to the measurement of the radiation sensor. This can undesirably reduce the accuracy of the detection.SUMMARY

[0006] An object of the invention is to improve the accuracy of the detection of radiation by a radiation sensor.

[0007] According to an aspect, there is provided a radiation sensor for detecting EUV radiation, the radiation sensor comprising: a radiation receiving side for receiving radiation to be detected; a substrate layer comprising a photodiode at the radiation receiving side; a cathode configured to collect charge from the photodiode; and a side shield configured to shield the photodiode from radiation entering the substrate layer from an opposite side of the side shield from the photodiode and / or to shield the cathode from charge migrating from an opposite side of the side shield from the cathode, wherein the side shield extends into the substrate layer from the radiation receiving side.

[0008] According to another aspect, there is provided a method for manufacturing a radiation sensor for detecting EUV radiation, the method comprising: providing a substrate layer; forming a photodiode in the substrate layer at a radiation receiving side of the radiation sensor; electrically connecting a cathode to the photodiode such that the cathode is configured to collect charge from the photodiode; and forming a side shield that extends into the substrate layer from the radiation receiving side, the side shield configured to shield the photodiode from radiation entering the substrate layer from an opposite side of the side shield from the photodiode and / or to shield the cathode from charge migrating from an opposite side of the side shield from the cathode.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:Figure 1 depicts a lithographic system comprising a lithographic apparatus and a radiation source;Figure 2 schematically depicts a radiation sensor;Figure 3 schematically depicts a plan view of the radiation sensor of Figure 2;Figure 4 schematically depicts the radiation sensor of Figure 2 with the photodiode exposed;Figure 5 schematically depicts an alternative radiation sensor;Figure 6 schematically depicts an alternative radiation sensor; andFigures 7-11 schematically depict steps of a method of manufacturing the radiation sensor of Figure 2.DETAILED DESCRIPTION

[0010] Figure 1 shows a lithographic system comprising a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate an EUV radiation beam B and to supply the EUV radiation beam B to the lithographic apparatus LA. The lithographic apparatus LA comprises an illumination system IL, a support structure MT configured to support a patterning device MA (e.g., a mask), a projection system PS and a substrate table WT configured to support a substrate W.

[0010] 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.

[0011] After being thus conditioned, the EU V radiation beam B interacts with the patterning deviceMA. 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 Figure 1, the projection system PS may include a different number of mirrors (e.g. six or eight mirrors).

[0012] 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.

[0013] 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.

[0014] 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.

[0015] In an embodiment the lithographic apparatus LA comprises at least one radiation sensor 20. The radiation sensor 20 is for measuring energy of EUV radiation. The radiation sensor 20 is for measuring the energy of the radiation of the EUV radiation beam B or the patterned EUV radiation B’ associated with EUV radiation (e.g. radiation having a wavelength within the range 4-20 nm). The radiation beam B and the patterned EUV radiation beam B’ may comprise combined radiation 15 including both EUV radiation and non-EUV radiation. The radiation sensor 20 is for measuring energy associated with the EUV radiation component of the combined radiation.

[0016] Figure 2 schematically depicts an embodiment of the radiation sensor 20. The radiation sensor 20 is for detecting EUV radiation. In an embodiment the radiation sensor 20 may be used for detecting other types of radiation, i.e. non-EUV radiation. The radiation sensor 20 is described below primarily in the context of detecting EUV radiation.

[0017] As shown in Figure 2, the radiation sensor 20 comprises a radiation receiving side 33. The radiation receiving side 33 is for receiving radiation to be detected. Figure 2 schematically shows radiation 30 to be detected. The radiation 30 enters the radiation sensor 20 at the radiation receiving side 33 of the radiation sensor 20. In an embodiment, the radiation 30 comprises the radiation beam B or the patterned EUV radiation B’.

[0018] As shown in Figure 2, in an embodiment the radiation sensor 20 comprises a substrate layer 21. The substrate layer 21 may be substantially planar. One of the major surfaces of the substrate layer21 may be oriented at the radiation receiving side 33 of the radiation sensor 20. In an embodiment the substrate layer 21 comprises a semiconductor. For example, in an embodiment the substrate layer 21 comprises silicon. Alternatively, the substrate layer 21 may comprise germanium.

[0019] As shown in Figure 2, in an embodiment the substrate layer 21 comprises a photodiode 26. The photodiode 26 is configured to receive the radiation 30. The photodiode 26 is configured to convert the received radiation 30 into charge. The photodiode 26 may produce current when it absorbs photons of the radiation 30. The photodiode 26 may be referred to as a photodetector or a transducer.

[0020] As shown in Figure 2, the photodiode 26 is at the radiation receiving side 33 of the radiation sensor 20. As shown in Figure 2, in an embodiment the photodiode 26 is at the radiation receiving side 33 of the substrate layer 21. The photodiode 26 may be formed at or near the upper surface of the substrate layer 21. The term “upper” is used to refer to the orientation as shown in Figure 2. The upper surface may correspond to the surface at which radiation 30 to be detected enters the radiation sensor 20.

[0021] By providing the photodiode 26 at the radiation receiving side 33, the radiation 30 to be detected is less likely to be absorbed before it reaches the photodiode 26. If the photodiode 26 were distanced from the radiation receiving side 33, then the radiation 30 would be more absorbed by the material of the substrate layer 21 before reaching the photodiode 26. This is particularly important for radiation that is generally easily absorbed, for example EUV radiation. An embodiment of the invention is expected to improve the accuracy of measuring radiation 30.

[0022] As shown in Figure 2, in an embodiment the radiation sensor 20 comprises a cathode 27. The cathode 27 is configured to collect charge from the photodiode 26. The charge output by the photodiode 26 may be collected at the cathode 27. Charge collected at the cathode 27 may be a measure of the radiation 30 to be detected. Electrons may move from the photodiode 26 towards the cathode 27, thereby producing a photocurrent.

[0023] As shown in Figure 2, in an embodiment the radiation sensor 20 comprises an electrical connection 28. The electrical connection 28 is configured to electrically connect the cathode 27 to the photodiode 26. In an embodiment the electrical connection 28 comprises one or more vias. In an embodiment the electrical connection 28 comprises electrical wiring, for example one or more electrical wires and / or traces.

[0024] As shown in Figure 2, in an embodiment the radiation sensor 20 comprises a side shield 29. The side shield 29 may be located to a side of the photodiode 26. In an embodiment the side shield 29 is configured to shield the photodiode 26 from radiation entering the substrate layer 21 from an opposite side of the side shield 29. For example, in the diagram shown in Figure 2, it is possible that some radiation may undesirably enter the radiation sensor 20 to the left of the side shield 29. Such radiation may be detected by the photodiode 26. Such radiation may be apart from the radiation 30 to be detected. For example, such radiation may be apart from the radiation beam B or the patterned EUV radiation B’.

[0025] As shown in Figure 2, in an embodiment the side shield 29 extends into the substrate layer 21 from the radiation receiving side 33. Part of the substrate layer 21 remains at the opposite side of the side shield 29 from the photodiode 26. The side shield 29 may be distanced from a radially outer perimeter of the radiation sensor 20. The side shield 29 may help to reduce the amount of radiation that undesirably contributes to what is detected by the photodiode 26. An embodiment of the invention is expected to improve the accuracy of detection of radiation by the radiation sensor 20.

[0026] By way of comparison, an alternative way of trying to shield the photodiode from incoming light from the side is to coat the side wall of the sensor, for example with aluminium. If the sensor side wall is coated, then the coating is generally non-uniform and may include pin holes, i.e. points where the side wall is exposed without the coating. This is at least partly because the side wall of the sensor may be rough. For example, the side wall may be rough due to a dicing process. As a result, light still partially penetrates through the side wall, thereby reducing the accuracy of the detection of radiation.

[0027] As shown in Figure 2, the side shield 29 may be located near the side wall of the radiation sensor 20. However, the side shield 29 is distanced from the side wall. The side shield 29 may better prevent radiation from undesirably penetrating through the side wall to reach the photodiode 26.

[0028] In an embodiment the side shield 29 is configured to shield the cathode 27 from charge migrating from the opposite side of the side shield 29. As shown in Figure 2, a portion of the substrate layer 21 remains on the opposite side of the side shield 29 from the photodiode 26 and the cathode 27. It is possible for radiation incident on this portion to result in pairs of electrons and holes being generated. Such electrons may be referred to as photo electrons. In an embodiment the side shield 29 is configured to reduce or prevent diffusion of photo electrons from the side wall to the cathode 27. An embodiment of the invention is expected to improve the accuracy of measurement by the radiation sensor 20.

[0029] As shown in Figure 2, in an embodiment the side shield 29 extends beyond the photodiode 26 in a direction away from the radiation receiving side 33. In the orientation shown in Figure 2, the radiation receiving side 33 is the top side. The side shield 29 extends in a direction away from the radiation receiving side 33 into the substrate layer 21. In the orientation shown in Figure 2, the direction away from the radiation receiving side 33 is the downward direction. The side shield 29 extends downwards to one side of the photodiode 26. The side shield 29 extends beyond the photodiode 26. The bottom of the side shield 29 is below the bottom of the photodiode 26. The side shield 29 extends further into the substrate layer 21 and the depth of the photodiode 26.

[0030] In an embodiment the side shield 29 extends into the substrate layer 21 from a light receiving side 33 by at least 5 pm, optionally at least 10 pm, optionally at least 20 pm, and optionally at least 50 pm. A greater depth of the side shield 29 into the substrate layer 21 generally reduces the contribution of the measurement that is due to radiation entering the radiation sensor 20 from the opposite side of the side shield 29. For every 10 pm of increased depth of the side shield 29, the contribution may be expected to reduce by a factor of 2.

[0031] In an embodiment the side shield 29 extends into the substrate layer 21 by a distance of at most 100 |im, optionally at most 50 pm, optionally at most 20 pm and optionally at most 10 pm. By reducing the depth of the side shield 29, the cost of manufacturing the radiation sensor 20 may be reduced. Furthermore, the structural integrity of the radiation sensor 20 may be increased.

[0032] As shown in Figure 2, in an embodiment the side shield 29 comprises a material 31. In an embodiment the material 31 is configured to absorb radiation. In an embodiment the material 31 is non-transparent to incoming radiation. The material 31 is configured to absorb rays of radiation incident on the side shield 29. In an embodiment the material 31 is configured to absorb substantially all types of radiation that may be incident on the radiation sensor 20. Any type of radiation may potentially contribute to the measurement made by the radiation sensor 20. It is desirable to reduce the possibility of any such radiation of any type that may enter the radiation sensor 20 from the opposite side of the side shield 29 contributing to the measurement.

[0033] In an embodiment the side shield 29 comprises a material configured to reflect radiation. For example, the material 31 of the side shield 29 may be reflective to at least some types of radiation. The side shield 29 may be configured to reflect rays of radiation incident on the side shield 29.

[0034] In an embodiment the side shield 29 comprises a metal. For example, the material 31 of the side shield 29 may be a metal. Such a metal may desirably absorb radiation. For example, in an embodiment the metal is tungsten. However, other types of metal may be used for the side shield 29. For example, molybdenum or chromium may be used.

[0035] As mentioned above, in an embodiment the side shield 29 comprises a metal. In an alternative embodiment the side shield 29 comprises an electrical insulator. An electrical insulator may shield the cathode 27 from charges migrating from the opposite side of the side shield 29.

[0036] As shown in Figure 2, in an embodiment the side shield 29 is located in a groove formed in the substrate layer 21. The material 31 is located in the groove so as to form the side shield 29. As shown in Figure 2, in an embodiment the side shield 29 substantially fdls the groove. That is, the material 31 that forms the side shield 29 substantially fdls the groove, so as to form the side shield 29. The side shield 29 may have a thickness substantially the same as the width of the groove in the substrate layer 21. The groove may be referred to as a trench. The side shield 29 may be a tungsten-fdled trench.

[0037] Figure 3 schematically depicts a plan view of the radiation sensor 20. The view shown in Figure 3 is taken from above the radiation sensor 20 shown in Figure 2. The view of Figure 3 is from the radiation receiving side 33 of the radiation sensor 20.

[0038] As shown in Figure 3, in an embodiment the side shield 29 substantially surrounds the photodiode 26 when viewed from the radiation receiving side 33. In Figure 3, the side shield 29 is shown in dashed lines because it may not be exposed due to the presence of a top shield 32, as shown in Figure 2. By substantially surrounding the photodiode 26, the side shield 29 may shield the photodiode 26 and / or the cathode 27 from radiation and / or photo electrons from all around the radiation sensor 21. However, in an alternative embodiment the side shield 29 is located on only one side, onlytwo sides, or only three sides out of four sides of the photodiode 26. Depending on the location of the radiation sensor 20, it may not be necessary to provide a side shield 29 at one or more sides of the photodiode 26.

[0039] As shown in Figure 3, in an embodiment the side shield 29 forms a rectangle in plan view. However, in an alternative embodiment, the side shield 29 may form a polygonal shape such as a pentagon, hexagon etc., or may be an ellipse such as a circle.

[0040] Figure 4 schematically depicts the radiation sensor 20 of Figure 2 in use. As shown in Figure 4, in an embodiment the photodiode 26 is exposed at the radiation receiving side 33 of the radiation sensor 20. The photodiode 26 may comprise an exposed surface 34 on which the radiation 30 is incident. In an embodiment a dielectric layer 25 is provided on the substrate layer 21. Part of the dielectric layer 25 may be removed so as to expose the photodiode 26 for use of the radiation sensor 20. By removing the dielectric layer 25, the absorption of the radiation 30 by the dielectric layer 25 may be reduced or eliminated.

[0041] As shown in Figure 2, in an embodiment the radiation sensor 20 comprises a lower shield 22. The lower shield 22 is located on an opposite side of the photodiode 26 from the radiation receiving side 33. The photodiode 26 is located between the lower shield 22 and the incident radiation 30. The lower shield 22 is configured to shield the photodiode 26.

[0042] In an embodiment the lower shield 22 is configured to shield the photodiode 26 from radiation from an opposite side of the lower shield 22. In the arrangement shown in Figure 2, the opposite side of the lower shield 22 is shown below the lower shield 22. The lower shield 22 may prevent radiation from below the lower shield 22 from reaching the photodiode 26. For example, the lower shield 22 may be configured to absorb radiation. In an embodiment the lower shield 22 is configured to reflect radiation. In an embodiment, radiation in a direction upwards in the orientation shown in Figure 2 may be substantially completely reflected by the lower shield 22.

[0043] In an embodiment the lower shield 22 is configured to shield the cathode 27 from charge migrating from the opposite side of the lower shield 22. For example, when radiation enters the radiation sensor 20 apart from via the radiation receiving side 33, the radiation that reaches the opposite side of the lower shield 22 (i.e. below the lower shield 22 shown in Figure 2) may cause photo electrons to be generated. In an embodiment the lower shield 22 is configured to block photo electrons from reaching the cathode 27. The lower shield 22 may be configured to function as a barrier preventing electron diffusion from below the lower shield 22 to the cathode 27.

[0044] As shown in Figure 2, in an embodiment the radiation sensor 20 comprises a further substrate layer 23. The further substrate layer 23 is in addition to the substrate layer 21 that comprises the photodiode 26. In an embodiment the base material for the further substrate layer 23 is substantially the same as that of the substrate layer 21. For example, in an embodiment the further substrate layer 23 is a semiconductor, for example silicon or germanium.

[0045] As shown in Figure 2, in an embodiment the lower shield 22 is located between the substrate layer 21 and the further substrate layer 23. In an embodiment a substrate 24 comprises the substrate layer 21, the lower shield 22 and the further substrate layer 23. In an embodiment the substrate 24 is a layered silicon-insulator-silicon substrate.

[0046] In an embodiment the lower shield 22 comprises an electrical insulator. For example, in an embodiment the electrical insulator is an oxide such as silicon dioxide. In an embodiment the substrate 24 is formed by silicon on insulator (SOI) technology. The lower shield 22 may be formed easily and cheaply during manufacture of the radiation sensor 20.

[0047] In an alternative embodiment the lower shield 22 comprises an electrical conductor. The electrical conductor may be configured to drain charges in the substrate. The electrical conductor may reduce the possibility of charges undesirably reaching the cathode 27.

[0048] By providing the lower shield 22, the possibility of unwanted radiation undesirably affecting a measurement by the photodiode 26 is reduced. An embodiment of the invention is expected to improve the accuracy of radiation sensors.

[0049] As shown in Figure 2, in an embodiment the lower shield 22 extends beyond the photodiode 26 when viewed from the radiation receiving side 33. In a plan view of the radiation sensor 20, the photodiode 26 may fit within the lower shield 22. For example, as shown in Figure 2, in an embodiment the lower shield 22 extends substantially across the whole of the substrate layer 21. The lower shield 22 provides an effective barrier against photo electrons migrating to the cathode 27.

[0050] As shown in Figure 2, in an embodiment the side shield 29 extends beyond the lower shield 22 in a direction away from the radiation receiving side 33. In the view shown in Figure 2, the side shield 29 extends below the lower shield 22. Part of the side shield 29 is located on the opposite side of the lower shield 22 from the photo diode 26. The side shield 29 may go through the lower shield 22. This helps to prevent radiation undesirably coupling into the lower shield 22.

[0051] By extending the side shield 29 beyond the lower shield 22, the contribution of photo current from stray radiation may be reduced by about 3 orders of magnitude compared to if the side shield 29 stops at the lower shield 22. An embodiment of the invention is expected to improve the accuracy of radiation measurement.

[0052] As shown in Figure 2, in an embodiment the radiation sensor 20 comprises an upper shield 32. The upper shield 32 may be referred to as a top shield. The upper shield 32 is configured to shield the photodiode 26 from radiation entering the radiation sensor 20 outside of a radiation receiving area at the radiation receiving side 33 of the radiation sensor 20. The radiation receiving area may correspond to a target area at the radiation receiving side 33 of the radiation sensor 20. For example, in the arrangement shown in Figure 3, the radiation receiving area may be defined by the radially inner edge of the upper shield 32.

[0053] As shown in Figure 2, the upper shield is located at the radiation receiving side 33 of the radiation sensor 20. For example, as shown in Figure 2, in an embodiment the upper shield 32 isprovided above the side shield 29. In an embodiment the side shield 29 and the upper shield 32 adjoin. For example, the material 31 of the side shield 29 may come into contact with the upper shield 32. By adjoining the side shield 29 with the upper shield 32, the possibility of radiation or photo electrons undesirably passing between the upper shield 32 and the side shield 29 may be reduced or eliminated.

[0054] As shown in Figure 3, in an embodiment the upper shield 32 substantially surrounds the radiation receiving area when viewed from the radiation receiving side 33. In an embodiment the upper shield 32 defines the radiation receiving area. The radiation receiving area is the area through which the radiation 30 passes so as to be incident on the photodiode 26. However, in an alternative embodiment, the upper shield 32 may extend around only one, only two or only three out of four sides of the radiation receiving area of the photodiode 26.

[0055] In an embodiment the upper shield not only surrounds but covers / overlaps a substantial area of the radiation receiving side of the radiation sensor 20. In an embodiment the upper shield 32 comprises a material configured to absorb radiation. For example, in an embodiment the upper shield 32 comprises metal. The upper shield 32 may be formed as a metal coating on an upper surface of the radiation sensor 20.

[0056] In an embodiment the side shield 29 and / or the upper shield 32 overlaps the whole area on the radiation receiving side 33 except for a target area. The target area may be where it is intended to capture the EUV radiation.

[0057] Figure 5 schematically depicts an alternative radiation sensor 20. Features of the radiation sensor 20 shown in Figure 5 which are the same as features of the radiation sensor 20 shown in Figure 2 are not described below. The features of the radiation sensor 20 shown in Figure 5 are the same as shown in Figure 2, with the following differences.

[0058] In the arrangement shown in Figure 2, the side shield 29 substantially fills the groove so as to form the side shield 29. However, as shown in Figure 5, in an alternative embodiment the side shield 29 is located at an inner surface of a groove formed in the substrate layer 21. The material 31 that forms the side shield 29 may be located at an inner surface of the groove. For example, as shown in Figure 5, in an embodiment the material 31 substantially lines the groove so as to form the side shield 29. An embodiment of the invention is expected to reduce the cost of materials to manufacture the radiation sensor 20.

[0059] In an embodiment the side shield 29 comprises a plurality of layers. The layers may be metal layers. In an alternative embodiment the layers may be a combination of dielectric layers and metal layers. The layers may be arranged as a stack of layers. In an embodiment the side shield 29 comprises an adhesive layer configured to adhere to the inner surface. In an embodiment the side shield 29 comprises one or more layers adjacent to the adhesive layer. The adhesive layer may be located between the inner surface and the one or more other layers. In an embodiment the adhesive layer comprise TiN. TiN is a higher adhesion material.

[0060] In the arrangement shown in Figure 2, the side shield 29 extends below the lower shield 22. However, in an alternative embodiment as shown in Figure 5, the side shield 29 may extend no further than the lower shield 22 in a direction away from the radiation receiving side 33. As shown in Figure 5, in an embodiment the side shield 29 and the lower shield 22 adjoin. By adjoining the side shield 29 to the lower shield 22, the possibility of radiation or photo electrons passing between the side shield 29 and the lower shield 22 may be reduced.

[0061] As shown in Figure 5, the upper shield 32 may be omitted. In an embodiment the side shield 29 is exposed at the radiation receiving side 33 of the radiation sensor 20.

[0062] Figure 6 schematically depicts an alternative radiation sensor 20. Features of the radiation sensor 20 shown in Figure 6 are the same as features described above with reference to Figure 2, except where otherwise below.

[0063] As shown in Figure 6, in an embodiment the substrate 24 consists of the substrate layer 21. The further substrate layer 23 may be omitted. As shown in Figure 6, the lower shield 22 may be omitted. An embodiment of the invention is expected to simplify manufacture of the radiation sensor 20.

[0064] As shown in Figure 2 and Figure 4, in an embodiment the substrate 24 comprises a first substrate layer 21 and a further substrate layer 23. In an embodiment the further substrate layer 23 is doped. For example, the further substrate layer 23 may be N-doped. By doping the further substrate layer 23, pairs of photo electrons and holes in the further substrate layer 23 may be neutralised such that the photo electrons are less likely to reach the cathode 27 associated with the photodiode 26. An embodiment of the invention is expected to improve the accuracy of measurement of a radiation sensor 20.

[0065] In an embodiment the radiation sensor 20 is for detecting EUV radiation. In an embodiment the radiation sensor 20 comprises a filter configured to filter out non-EUV radiation received at the radiation receiving side 33. In an embodiment the filter is configured to prevent non-EUV radiation reaching the photodiode 26. For example, in an embodiment the exposed surface 34 of the photodiode 26 comprises the filter. In an embodiment the filter is a band pass filter. In an embodiment the filter comprises a material selected from a group consisting of Zr, poly-Si, Al, Ti, TiN, W and multilayers comprising one or more of Zr, poly-Si, Al, Ti, TiN and W.

[0066] In an embodiment the substrate table WT is provided with at least one radiation sensor 20. In an embodiment the radiation sensor 20 is located radially outward of the substrate W. In an embodiment a plurality of radiation sensors 20 are provided in the substrate table WT. by providing the radiation sensors 20 at the substrate table WT, the radiation sensor 20 may determine the energy of EUV radiation that reaches the level of the substrate W. this may help to improve the accuracy of the measurement of energy of EUV radiation that reaches the substrate W. Additionally or alternatively, the radiation sensor 20 may be located at other positions along the optical path between the radiation source SO and the substrate table WT. For example, in an embodiment the lithographic apparatus LAcomprises at least one sensor 20 at or near the intermediate focus point (i.e. where the radiation beam B enters the illumination system IL shown in Figure 1). In an embodiment a radiation sensor 20 is provided at or near the faceted field mirror device 10. In an embodiment at least one radiation sensor 20 is provided at or near the faceted pupil mirror device 11. In an embodiment at least one radiation sensor 20 is provided at or near the support structure MT. In an embodiment at least one radiation sensor 20 is provided at or near at least one of the plurality of mirrors 13, 14 of the projection system PS. An embodiment of the invention is expected to improve monitoring of system power at one or more modules of the lithographic apparatus LA.

[0067] In an embodiment the radiation sensor 20 is provided substantially coplanar with the substrate W.

[0068] Figures 7-11, 2 and 4 schematically depict steps of a method for manufacturing a radiation sensor 20. In an embodiment the method comprises providing a substrate layer 21. For example, as shown in Figure 7, in an embodiment a substrate 24 is provided. The substrate 24 may be a layered silicon-insulator-silicon substrate.

[0069] In an embodiment the method comprises oxidising a surface of the first substrate 21 so as to form the lower shield 22. The oxidised first substrate layer 21 is then bonded, for example by wafer bonding, to the further substrate layer 23. Alternatively, the method may comprise oxidising the further substrate layer 23 and then bonding the oxidised further substrate layer 23 to the substrate layer 21. Alternatively, the lower shield 22 may be formed by ion beam implantation.

[0070] As shown in Figure 8, in an embodiment the method comprises forming a photodiode 26 in the substrate layer 21. The photodiode 26 is formed at the radiation receiving side 33 of the radiation sensor 20, for example at the radiation receiving side 33 of the substrate layer 21. In an embodiment the step of forming the photodiode 26 comprises an ion implantation process to form the photodiode 26.

[0071] As shown in Figure 9, in an embodiment the method comprises electrically connecting a cathode 27 to the photodiode 26 such that the cathode 27 is configured to collect charge from the photodiode 26. In an embodiment a dielectric layer 25 (e.g. an oxide) may be provided at the radiation receiving side 33 of the substrate layer 21. The cathode 27 may be located within the dielectric layer25. In an embodiment an electrical connection 28 is formed between the cathode 27 and the photodiode26.

[0072] As shown in Figure 10, in an embodiment the method comprises forming a groove 35 in the substrate layer 21. As shown in Figure 10, in an embodiment the groove 35 extends through the dielectric layer 25 and part of the way through the substrate 24. In an embodiment the step of forming the groove 35 comprises an etching process, such as a reactive ion etching process.

[0073] As shown in Figure 11, in an embodiment the method comprises forming the side shield 29 that extends into the substrate layer 21 from the radiation receiving side 33. The side shield 29 is configured to shield the photodiode 26 from radiation entering the substrate layer 21 from an oppositeside of the side shield 29. In an embodiment the material 31 is deposited into the grooves 35 so as to form the side shield 29. In an embodiment the material 31 is deposited conformally. Material remaining at a top surface of the device may be removed, for example by etching and / or by chemical mechanical polishing.

[0074] As shown in Figure 2, in an embodiment the method comprises providing an upper shield 32. The upper shield 32 may be provided over the top of the side shield 29. In an embodiment the upper shield 32 is formed by a coating method.

[0075] As shown in Figure 4, in an embodiment the method comprises etching part of the dielectric layer 25 so as to expose an exposed surface 34 of the photodiode 26 at a radiation receiving area.

[0076] In an embodiment the further substrate 23 is doped to have a doping concentration of at least 2xl018cm-3, optionally at least 5xl018cm-3, optionally at least lxl019cm-3, optionally at least 2xl019cm-3, and optionally at least 5xl019cm-3.

[0077] As shown in Figure 3, in an embodiment the radiation sensor 20 comprises one photodiode 26. The side shield 29 surrounds only one photodiode 26. In an alternative embodiment, the radiation sensor 20 may comprise a plurality of photodiodes 26. The photodiodes 26 may be provided so as to be protected by the same side shield 29. The side shield 29 may be formed to surround a plurality of photodiodes 26.

[0078] 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, liquidcrystal displays (LCDs), thin-film magnetic heads, etc.

[0079] 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.

[0080] 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 certainactions. 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.

[0081] 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.

Claims

CLAIMS1. A radiation sensor for detecting EUV radiation, the radiation sensor comprising: a radiation receiving side for receiving radiation to be detected; a substrate layer comprising a photodiode at the radiation receiving side; a cathode configured to collect charge from the photodiode; and a side shield configured to shield the photodiode from radiation entering the substrate layer from an opposite side of the side shield from the photodiode and / or to shield the cathode from charge migrating from an opposite side of the side shield from the cathode, wherein the side shield extends into the substrate layer from the radiation receiving side.

2. The radiation sensor of claim 1, wherein the side shield extends beyond the photodiode in a direction away from the radiation receiving side.

3. The radiation sensor of claim 1 or 2, wherein the side shield comprises a material configured to absorb radiation.

4. The radiation sensor of any preceding claim, wherein the side shield comprises a material configured to reflect radiation.

5. The radiation sensor of any preceding claim, wherein the side shield comprises a metal.

6. The radiation sensor of claim 5, wherein the metal is tungsten.

7. The radiation sensor of any preceding claim, wherein the side shield comprises an electrical insulator.

8. The radiation sensor of any preceding claim, wherein the side shield is located at an inner surface of a groove formed in the substrate layer.

9. The radiation sensor of claim 8, wherein the side shield substantially fills the groove.

10. The radiation sensor of any preceding claim, wherein the side shield substantially surrounds the photodiode when viewed from the radiation receiving side.

11. The radiation sensor of any preceding claim, comprising: a lower shield located on an opposite side of the photodiode from the radiation receiving sideof the radiation sensor.

12. The radiation sensor of claim 11, wherein the lower shield is configured to shield the photodiode from radiation from an opposite side of the lower shield.

13. The radiation sensor of claim 11 or 12, wherein the lower shield is configured to shield the cathode from charge migrating from an opposite side of the lower shield.

14. The radiation sensor of any of claims 11-13, wherein the lower shield extends beyond the photodiode when viewed from the radiation receiving side.

15. The radiation sensor of any of claims 11-14, wherein the side shield and the lower shield adjoin.

16. The radiation sensor of any of claims 11-15, wherein the side shield extends beyond the lower shield in a direction away from the radiation receiving side.

17. The radiation sensor of any of claims 11-16, wherein the lower shield comprises an electrical insulator.

18. The radiation sensor of claim 17, wherein the electrical insulator is silicon dioxide.

19. The radiation sensor of any of claims 11-16, wherein the lower shield comprises an electrical conductor.

20. The radiation sensor of any of claims 11-19, comprising a further substrate layer, wherein the lower shield is located between the substrate layers.

21. The radiation sensor of claim 20, wherein the further substrate layer is doped.

22. The radiation sensor of any preceding claim, comprising an upper shield configured to shield the photodiode from radiation entering the radiation sensor outside of a radiation receiving area at the radiation receiving side of the radiation sensor, wherein the upper shield is located at the radiation receiving side of the radiation sensor.

23. The radiation sensor of claim 22, wherein the side shield and the upper shield adjoin.

24. The radiation sensor of claim 22 or 23, the upper shield substantially surrounds the radiation receiving area when viewed from the radiation receiving side.

25. The radiation sensor of any preceding claim, comprising a fdter configured to filter out non- EUV radiation received at the radiation receiving side from reaching the photodiode.

26. A stage for an EUV lithography apparatus, the stage configured to support a reticle or a substrate and comprising the radiation sensor of any preceding claim.

27. An EUV lithographic apparatus comprising the radiation sensor of any of claims 1-25 or the stage of claim 26.

28. A method for manufacturing a radiation sensor for detecting EUV radiation, the method comprising: providing a substrate layer; forming a photodiode in the substrate layer at a radiation receiving side of the radiation sensor; electrically connecting a cathode to the photodiode such that the cathode is configured to collect charge from the photodiode; and forming a side shield that extends into the substrate layer from the radiation receiving side, the side shield configured to shield the photodiode from radiation entering the substrate layer from an opposite side of the side shield from the photodiode and / or to shield the cathode from charge migrating from an opposite side of the side shield from the cathode.

29. The method of claim 28, wherein the photodiode is formed such that it extends less far than the side shield in a direction away from the radiation receiving side.

30. The method of claim 28 or 29, wherein forming the side shield comprises: forming a groove in the substrate layer.

31. The method of claim 30, wherein forming the side shield comprises: applying a material to an inner surface of the groove.

32. The method of claim 30 or 31, wherein forming the side shield comprises: substantially filling the groove with a material.

33. The method of claim 31 or 32, wherein the material comprises metal.

34. The method of any of claims 30-33, wherein the groove is formed so as to substantially surround a region where the photodiode is formed when viewed from the radiation receiving side.

35. The method of any of claims 28-34, wherein providing the substrate layer comprises: providing a substrate comprising the substrate layer, a lower shield and a further substrate layer, wherein the lower shield is between the substrate layers.

36. The method of claim 35, wherein the lower shield extends across substantially all of the substrate.

37. The method of claims 35 or 36, wherein the side shield is formed so as to adjoin the lower shield.

38. The method of claim 37, wherein the side shield is formed so as to extends beyond the lower shield in a direction away from the radiation receiving side.

39. The method of any of claims 35-38, comprising: doping the further substrate layer.

40. The method of any of claims 28-39, comprising: forming an upper shield at the radiation receiving side of the radiation sensor, wherein the upper shield is configured to shield the photodiode from radiation entering the radiation sensor outside of a radiation receiving area at the radiation receiving side of the radiation sensor.

41. The method of claim 40, wherein forming the upper shield comprises: applying a metal layer over the side shield at the radiation receiving side.

42. The method of any of claims 28-41, comprising: applying a dielectric layer to the substrate layer at the radiation receiving side.

43. The method of claim 42, wherein the side shield is formed to extend through the dielectric layer.

44. The method of claim 42 or 43, comprising: removing an area of the dielectric layer such that the photodiode is exposed at the radiation receiving side of the radiation sensor.

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