Metrology apparatus

Abstract

The invention provides a metrology apparatus. The metrology apparatus comprises a mass metrology station for measuring a mass and / or a change in mass of a wafer, and a spectral imaging system for performing spectral imaging of at least part of a wafer.

Description

[0001] METROLOGY APPARATUS

[0002] Field of the Invention

[0003] The present invention relates to a metrology apparatus for performing mass metrology and spectral imaging and particularly, although not exclusively, to a metrology apparatus for semiconductor wafer metrology.

[0004] Background

[0005] Electronic devices are fabricated on substrates such as semiconductor wafers using a variety of processing techniques such as deposition, etching, cleaning and / or other treatments. Examples of deposition techniques include chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), etc. Examples of removal or etching techniques include stripping, wet etching, dry etching, chemical mechanical polishing (CMP), etc.

[0006] These substrate treatments typically cause changes to a side or surface of the substrate and / or to the mass of the substrate. For example, deposition generally increases the mass of the substrate while etching generally decreases the mass of the substrate. During production, it is desirable to assess the substrates to determine whether processing is being performed correctly and / or to adjust the process prior to production of subsequent substrates.

[0007] Such an assessment of a substrate can be performed by measuring the mass and / or the change in mass of the substrate during processing. For example, the mass of the substrate may be measured before and after a specific processing step, and the change in mass of the substrate caused by the processing step can be used to determine whether the processing step is being performed correctly and / or to adjust the processing step prior to production of subsequent substrates.

[0008] Mass metrology apparatuses are available that can provide high accuracy measurement of the mass and / or the change in mass of a substrate during processing. Such mass metrology apparatuses can therefore be used to provide high-accuracy monitoring of processing of substrates.

[0009] However, measuring the mass and / or the change in mass of the substrate alone may not enable a complete assessment of the substrate to be performed. For example, a measurement of the mass and / or the change in mass of the substrate during processing only provides a single measurement result for the whole substrate, and therefore does not provide any spatial or uniformity information regarding the processing. For example, for a given mass of material deposited on the side or surface of the substrate, the measured mass and / or change in mass will be the same regardless of the distribution of the deposited material on the side or surface of the substrate.

[0010] It is also known to assess the uniformity of a side or surface of a substrate using optical metrology techniques. For example, a plurality of optical sensors and a spectrometer can be used to obtain spectra from the side or surface of the substrate at a plurality of discrete measurement locations on the side or surface of the substrate. The plurality of spectra can be used to assess the uniformity of the side or surface of the substrate and to obtain substrate uniformity information, for example a uniformity map of the side or surface of the substrate.

[0011] Typically, the side or surface of the substate is a front, top, upper or main side or surface of the substrate. It may alternatively be referred to as a front, top, upper or main face of the substrate.

[0012] Furthermore, typically the side or surface of the substrate is a side or surface on which a device is provided or is being manufactured.

[0013] US 10,989,652 B2 discloses a metrology system for substrate processing that includes a mass metrology station that measures the mass and / or the mass change of the substrate. In addition, the metrology system further includes a standalone optical metrology station that includes a plurality of optical sensors and a spectrometer to measure spectra from a plurality of measurement locations on a substrate. The metrology system further comprises a controller that includes a modelling module to generate thickness values at the plurality of measurement locations based on the spectra from the plurality of measurement locations and a learned model. The controller further includes a spatial modelling module that generates a spatial thickness distribution model for the substrate based on the thickness values at the plurality of measurement locations from the modelling module and the mass and / or the mass change from the mass metrology station.

[0014] Therefore, in US 10,989,652 B2, measurement data obtained for the substrate in the mass metrology station and measurement data obtained for the substrate in the standalone optical metrology station are both used to assess the substrate. For example, the measurement data obtained from the standalone optical metrology station may provide spatial or uniformity information regarding the processing that is absent from the measurement data obtained from the mass metrology station. This combination of different types of measurement data therefore allows better monitoring of processing of the substrate than either mass metrology or optical metrology alone.

[0015] The present invention has been devised in light of the above considerations.

[0016] Summary of the Invention

[0017] According to a first aspect of the present invention there is provided a metrology apparatus comprising: a mass metrology station for measuring a mass and / or a change in mass of a wafer; and a spectral imaging system for performing spectral imaging of at least part of a wafer.

[0018] Therefore, in the first aspect of the present invention, the metrology apparatus includes both a mass metrology station for measuring the mass and / or change in mass of a wafer and a spectral imaging system for performing spectral imaging of at least part of the wafer. Therefore, the apparatus can be used to determine both the mass and / or change in mass of the wafer and to obtain spectral imaging data of the wafer.

[0019] Integrating the mass metrology station and the spectral imaging system into a single apparatus may provide a number of advantages. For example, a footprint of the apparatus may be smaller than the footprint would be if a standalone mass metrology station and a standalone spectral imaging station were provided. A cost of producing the apparatus may also be less than the cost would be if a standalone mass metrology station and a standalone spectral imaging station were provided.

[0020] Spectral imaging data for a wafer and the mass and / or change in mass for the wafer may be combined synergistically to provide more detailed information regarding one or more parameters of the wafer than can be determined from the spectral imaging data alone or from the mass and / or change in mass alone.

[0021] For example, the mass and / or change in mass may be used as a constraint when determining uniformity data for the wafer from the spectral imaging data, to obtain more accurate uniformity data for the wafer.

[0022] Alternatively, or in addition, the spectral imaging data may be used to provide uniformity data in addition to the measured mass and / or change in mass. For example, the spectral imaging data may be used to determine the uniformity of a pattern of interest, for example the thickness or a critical dimension (for example the size of a specific feature). The uniformity of the pattern of interest may indirectly point to the mass distribution, for example.

[0023] Measurement of the mass and / or change in mass of the wafer by the mass metrology station may be highly sensitive to one or more of vibration, electromagnetic noise and temperature variations. A spectral imaging system may be able to perform spectral imaging of at least part of the wafer with minimal movement of the spectral imaging system and / or any components of the spectral imaging system, for example when compared to other types of optical metrology systems. The spectral imaging system may therefore not significantly adversely affect measurements by the mass metrology station.

[0024] The mass metrology apparatus according to the first aspect of the present invention may have any one, or, where compatible, any combination of the following optional features.

[0025] The mass metrology station and spectral imaging system are integrated into a single apparatus.

[0026] The mass metrology station and spectral imaging system may be integrated together, and / or connected together, and / or attached together, and / or fixed together, either directly or indirectly via one or more other parts or components or stations of the apparatus.

[0027] The mass metrology station and spectral imaging system may be included in, or on, a single housing or enclosure or casing.

[0028] The spectral imaging system may be for performing spectral imaging of at least part of a side or surface of the wafer.

[0029] The side or surface of the wafer may be a front, top, upper or main side or surface of the wafer. It may alternatively be referred to as a front, top, upper or main face of the wafer.

[0030] The side or surface of the wafer may be a side or surface of the wafer on which a device is provided, or on which a device is being manufactured.

[0031] The spectral imaging system may be for performing spectral imaging of a side or surface (for example a front, top, upper or main side or surface) of the wafer. Performing spectral imaging of at least part of the wafer may comprise obtaining spectral imaging data for at least part of the wafer.

[0032] Performing spectral imaging of at least part of the wafer may comprise obtaining optical spectral imaging data for at least part of the wafer.

[0033] Performing spectral imaging of at least part of the wafer may comprise obtaining a spectral image of at least part of the wafer.

[0034] Performing spectral imaging of at least part of the wafer may comprise obtaining an optical spectral image of at least part of the wafer.

[0035] Spectral imaging may comprise acquiring optical spectral information across every point on an image, for example every pixel of an image. It may be a generic term referring to the combination of spectroscopy and imaging. The optical spectral information may be acquired for only part of the optical spectrum, or for the entire optical spectrum.

[0036] A spectral image may therefore comprise an optical spectrum, or partial optical spectrum, at each pixel of the image.

[0037] Spectral imaging may comprise obtaining intensity data over a specific wavelength range for each point or pixel in an image, for example a wavelength range of 400-1000 nm.

[0038] As discussed below, multispectral imaging and hyperspectral imaging are two subsets of spectral imaging.

[0039] Spectral imaging may mean imaging that uses multiple wavelengths or bands of wavelength across the electromagnetic spectrum, for example multiple wavelengths or bands of wavelengths across the visible spectrum or optical spectrum.

[0040] For example, the spectral imaging system may use wavelengths in the visible to near-infrared range, for example wavelengths in the range of 400nm to 10OOnm. Of course, wavelengths above or below this range of wavelengths may also be used in addition.

[0041] The spectral imaging system may use wavelengths in the visible to mid-infrared range, for example wavelengths in the range of 400 nm to 8000nm. Of course, wavelengths above or below this range of wavelengths may also be used in addition.

[0042] The spectral imaging system may use wavelengths in the optical spectrum.

[0043] Spectral imaging may mean obtaining imaging data in which a spectrum (for example an optical spectrum) is obtained for each (every) pixel in an image.

[0044] A spectral image may be an image in which a spectrum (for example an optical spectrum) is included for each (every) pixel in the image.

[0045] Spectral imaging data may be imaging data in which a spectrum (for example an optical spectrum) is included for each (every) pixel in an image. The spectrum typically covers a predetermined spectral range.

[0046] Spectral imaging may mean obtaining an image or imaging data in which intensity versus wavelength (or frequency) data is obtained for each pixel of the image.

[0047] A spectral image may be an image in which intensity versus wavelength (or frequency) data is included for each (every) pixel of the image.

[0048] Spectral imaging data may be imaging data in which intensity versus wavelength (or frequency) data is included for each (every) pixel of the image.

[0049] Spectral imaging data may mean spectral reflectance data, for example optical spectral reflectance data.

[0050] The obtained spectrum may be a continuous spectrum over a predetermined spectral range, for example comprising a plurality of contiguous wavelengths or wavelength bands. Alternatively, the obtained spectrum may be a non-continuous spectrum over a predetermined spectral range, for example comprising a plurality of wavelengths or wavelength bands at least some of which are non-contiguous.

[0051] For example, such a spectrum may comprise more than or equal to 5, or more than or equal to 10, or more than or equal to 15, or more than or equal to 20, or more than or equal to 30, or more than or equal to 40, or more than or equal to 50, or more than or equal to 100, wavelengths or wavelength bands, which may be contiguous and / or non-contiguous. The number of wavelengths or wavelength bands may be less than or equal to 1000, or less than or equal to 500, or less than or equal to 300, or less than or equal to 200, for example.

[0052] A spectral image may correspond to, or illustrate, or measure, a spectroscopic reflectance of the side or surface of the wafer, for example at all areas of the side or surface of the wafer, or at all areas of part of the side or surface of the wafer.

[0053] Performing spectral imaging of the wafer may correspond to, or comprise, measuring spectroscopic reflectance of a whole side or surface of the wafer or part of the side or surface of the wafer.

[0054] Performing spectral imaging may comprise obtaining a plurality of different images for or with a respective plurality of different wavelengths or ranges or bands of wavelengths of illumination (i.e. each of the plurality of different images being obtained for or with a different wavelength or range or band of wavelength of illumination).

[0055] Performing spectral imaging may comprise obtaining a single image for a plurality of different wavelengths or ranges or bands of wavelengths of illumination (i.e. a single image obtained for a plurality of different wavelengths or ranges or bands of wavelengths of illumination simultaneously).

[0056] The spectral imaging system may be an optical spectral imaging system.

[0057] The spectral imaging system may be a multispectral imaging system or a hyperspectral imaging system.

[0058] Multispectral imaging and hyperspectral imaging are both examples of spectral imaging.

[0059] Multispectral imaging (which may alternatively be referred to as multiband imaging) may comprise acquisition of intensity at multiple wavelengths or wavelength bands over a predetermined spectral range. The multiple wavelengths or wavelength bands may or may not be contiguous wavelengths or wavelength bands. Typically, the number of wavelengths or wavelength bands is in the range of 5-15 over the predetermined spectral range, but more or fewer may be used. For example, in one specific example a multispectral imaging system may acquire data over the spectral range 400-1000 nm at 6 wavelength bands with a bandwidth of 50nm at steps of 100nm. For instance, bands centred at 450 nm, 550 nm, 650 nm, 750 nm, 850 nm, 950 nm.

[0060] As with multispectral imaging, hyperspectral imaging may comprise acquisition of intensity at multiple wavelengths or wavelength bands over a predetermined spectral range. The multiple wavelengths or wavelength bands are typically contiguous wavelengths or wavelength bands, so that the obtained spectrum is a continuous spectrum. Typically, the number of wavelengths or wavelength bands used is in the range of 50 - 250 over the predetermined spectral range, but more or fewer may be used. For example, in one specific example a hyperspectral imaging system may acquire data over a spectral range of 400 - 10OOnm at 120 wavelengths or contiguous wavelength bands of bandwidth 5 nm.

[0061] A primary difference between hyperspectral imaging and multispectral imaging may therefore be that hyperspectral imaging uses a larger number of narrower wavelengths or wavelength bands than multispectral imaging, thereby providing more detail and / or a higher spectral resolution for each pixel of the image than multispectral imaging.

[0062] As mentioned above, the term spectral imaging includes both multispectral imaging and hyperspectral imaging.

[0063] Hyperspectral imaging may comprise obtaining hyperspectral cube data, or a hyperspectral data cube, for at least part of the side or surface of the wafer.

[0064] Hyperspectral imaging data may comprise a hyperspectral data cube.

[0065] The metrology apparatus may be configured to generate wafer uniformity data based on at least an output of the spectral imaging system for the wafer.

[0066] Uniformity data may indicate the uniformity of one or more parameters of the wafer across the side or surface of the wafer.

[0067] Uniformity data may indicate the uniformity of one or more dimensions of the wafer across the side or surface of the wafer. The one or more dimensions may be one or more dimensions of a layer or pattern of interest on the wafer.

[0068] For example, the uniformity data may relate to the uniformity of one or more of a thickness of a layer on the side or surface of the wafer, or a critical dimension of a pattern on the side or surface of the wafer, or the uniformity of a pattern of interest across the side or surface of the wafer.

[0069] Uniformity data may comprise one or more of thickness data, critical dimension data, depth data and material density data. The metrology apparatus may be configured to generate wafer uniformity data based on both the output of the spectral imaging system for the wafer and the mass and / or change in mass measurement for the wafer.

[0070] The metrology apparatus may be configured to use a learned model, or a machine learning model, to generate the wafer uniformity data.

[0071] For example, the learned model, or machine learning model, may relate uniformity data to the spectral imaging data.

[0072] The learned model, or machine learning model, may be generated using machine learning, for example. The machine learning may include a supervised learning model selected from the group consisting of linear models, support vector machine models, decision tree models, random forest models and Gaussian models for example.

[0073] The learned model, or machine learning model, may be generated by correlating spectral imaging data and / or mass and / or change in mass for a wafer or wafers to uniformity data for the wafer or wafers, for example wherein the uniformity data includes at least one of thickness data, critical dimension data, depth data and material density data, which for example may be accurately measured using one or more known metrology methods. Alternatively, uniformity data may be determined by unsupervised learning. For example, based on a clustering operation on optical spectral data from different locations on the wafer.

[0074] The spectral imaging system may be configured to perform spectral imaging of at least part of the wafer while the wafer is in the mass metrology station.

[0075] Therefore, the spectral imaging system may be integrated with, or into, the mass metrology station.

[0076] For example, part or all of the spectral imaging system may be inside or within the mass metrology station.

[0077] Integrating the mass metrology station and spectral imaging system in this manner may reduce an amount of time required to obtain the spectral imaging data and the mass and / or change in mass compared to measuring these in separate locations.

[0078] The mass metrology station may comprise a device for measuring the weight or mass, and / or the change in weight or mass, of a wafer, and the spectral imaging system may be configured to perform spectral imaging of at least part of the wafer while the wafer is loaded on the device.

[0079] For example, the device may comprise a load cell and a pan or support for supporting the wafer during a measurement, and the spectral imaging system may be configured to perform spectral imaging of at least part of the wafer while the wafer is loaded on the pan or support.

[0080] The metrology apparatus may comprise a thermalisation station for changing the temperature of a wafer.

[0081] For example, it is advantageous that the wafer has the same temperature as the mass metrology station when the wafer is loaded into the mass metrology station. Otherwise, a difference in temperature between the wafer and the mass metrology station may cause issues such as convention currents inside the mass metrology station, or a change in the temperature of the air in the mass metrology station and therefore a change in a buoyance force experienced by the wafer. These issues can negatively affect the accuracy of the measurement of the mass and / or change in mass of the wafer.

[0082] The thermalisation station may therefore be for changing the temperature of the wafer to a predetermined temperature, and / or for causing a predetermined change in the temperature of the wafer.

[0083] The thermalisation station may be for equalising the temperature of the wafer to a predetermined temperature.

[0084] Typically, the temperature of the wafer when placed on the thermalisation station is greater than the predetermined or desired temperature of the wafer. In such a case the thermalisation station will therefore cool the wafer to the desired or predetermined temperature. Of course, alternatively the temperature of the wafer when placed on the thermalisation station may be less than the predetermined or desired temperature of the wafer. In such a case the thermalisation station will therefore heat the wafer to the desired or predetermined temperature.

[0085] The spectral imaging system may be configured to perform spectral imaging of at least part of the wafer while the wafer is in the thermalisation station.

[0086] Integrating the thermalisation station and spectral imaging system in this manner may reduce an amount of time required to obtain the spectral imaging data and to change the temperature of the wafer compared to performing these steps separately.

[0087] The thermalisation station may comprise a temperature changing device or temperature changing part for changing the temperature of the wafer, and the spectral imaging system may be configured to perform spectral imaging of at least part of the wafer while the wafer is loaded on the temperature changing device or part.

[0088] For example, the temperature changing device or part may comprise a thermal transfer plate, which may be a plate or block of material, and the spectral imaging system may be configured to perform spectral imaging of at least part of the wafer while the wafer is on the thermal transfer plate.

[0089] The temperature changing device or part may comprise: a passive temperature changing device or part; or an active temperature changing device or part.

[0090] A passive temperature changing device or part may mean a device or part that does not have any powered heating or cooling devices.

[0091] An active temperature changing device or part may mean a device or part that has one or more powered heating or cooling devices, for example Peltier devices.

[0092] The apparatus may comprise a wafer handling system for loading a wafer into the mass metrology station and for loading a wafer into the thermalisation station. The wafer handling system may also unload wafers from the mass metrology station and the thermalisation station.

[0093] There may be a single wafer handling system. The wafer handling system may comprise one or more robotic arms. The, or each, robotic arm may comprise one or more end effectors for supporting or holding a wafer.

[0094] The mass metrology station and first thermalisation station may be arranged in a stack, i.e. a vertical stack.

[0095] The metrology apparatus may comprise more than one thermalisation station. For example, the metrology apparatus may comprise a first thermalisation station and a second thermalisation station.

[0096] The wafer handling system may be for loading a wafer into the mass metrology station and for loading a wafer into the first thermalisation station and for loading a wafer into the second thermalisation station.

[0097] The spectral imaging system may be configured to perform spectral imaging of at least part of the wafer while the wafer is in the first thermalisation station; or the spectral imaging system may be configured to perform spectral imaging of at least part of the wafer while the wafer is in the second thermalisation station.

[0098] The first thermalisation station may be an active thermalisation station and the second thermalisation station may be a passive thermalisation station.

[0099] The apparatus may be configured to convey a wafer to the first thermalisation station, and then from the first thermalisation station to the second thermalisation station, and then from the second thermalisation station to the mass metrology station.

[0100] The second thermalisation station may be configured to change the temperature of the wafer to be equal to, or substantially equal to, or within a predetermined temperature of, a temperature of the mass metrology station.

[0101] The metrology apparatus may comprise a spectral imaging station comprising the spectral imaging system.

[0102] The spectral imaging station may comprise a housing or chamber for housing at least part of the spectral imaging system.

[0103] The spectral imaging station may comprise a support for supporting a wafer during spectral imaging of at least part of the wafer. For example, the support may be a chuck or plate or block of material.

[0104] The spectral imaging station and the mass metrology station are integrated into a single apparatus.

[0105] The mass metrology station and spectral imaging station may be integrated together, and / or connected together, and / or attached together, and / or fixed together, either directly or indirectly via one or more other parts or components or stations of the apparatus.

[0106] The mass metrology station and the spectral imaging station may be arranged in a stack, i.e. a vertical stack.

[0107] The mass metrology station and spectral imaging station may be included in, or on, a single housing or enclosure or casing. The metrology apparatus may comprise a wafer handling system for loading the wafer into the mass metrology station and for loading the wafer into the spectral imaging station. The wafer handling system may also be for loading the wafer into any thermalisation stations that are included in the apparatus, for example a first thermalisation station or first and second thermalisation stations.

[0108] There may be a single wafer handling system.

[0109] The wafer handling system may comprise one or more robotic arms. The, or each, robotic arm may comprise one or more end effectors for supporting or holding a wafer.

[0110] The spectral imaging system may comprise a detector for obtaining spectral imaging data.

[0111] The detector may comprise a camera, for example a spectral imaging camera, for example a multispectral imaging camera or a hyperspectral imaging camera.

[0112] The spectral imaging system may comprise: an illumination source; a detector for obtaining spectral imaging data.

[0113] The spectral imaging system may further comprise optics configured to direct illumination from the illumination source onto a wafer, and to direct reflected illumination from the wafer to the detector.

[0114] The illumination source may emit illumination having wavelengths in the visible to near-infrared range, for example in the range of 400nm to 1000nm. Of course, wavelengths above or below this range of wavelengths may also be used in addition.

[0115] The illumination source may emit illumination having wavelengths in the visible to mid-infrared range, for example in the range of 400 nm to 8000nm. Of course, wavelengths above or below this range of wavelengths may also be used in addition.

[0116] The illumination may comprise or be light.

[0117] The illumination source may comprise or be a light source.

[0118] The detector may obtain spectral imaging data from the reflected illumination from the wafer.

[0119] The detector may acquire spectral reflectance data from at least part of the wafer, for example at least part of a side or surface of the wafer.

[0120] The illumination typically comprises light, i.e. visible light.

[0121] The illumination source may comprise a single broadband light source or multiple narrower broadband light sources which could be, but are not limited to, halogen, Xenon-arc or LEDs.

[0122] The optics may comprise one or more of a beam splitter, a lens or lenses, a polariser or polarisers, focussing optics, and / or a mirror or mirrors. The specific configuration of the optics is not essential to the present invention and various different arrangements and configurations are possible. The arrangements disclosed here are illustrative examples only. The detector may comprise a spectral imaging camera or a hyperspectral imaging camera. References to a hyperspectral imaging camera in the following may therefore be replaced with reference to a spectral imaging camera, unless incompatible.

[0123] A spectral imaging camera means a camera that is configured to perform spectral imaging and / or to obtain a spectral image and / or to obtain spectral imaging data.

[0124] A hyperspectral imaging camera means a camera that is configured to perform hyperspectral imaging and / or to obtain a hyperspectral image and / or to obtain hyperspectral imaging data.

[0125] The hyperspectral imaging camera may be configured to perform hyperspectral imaging of, and / or obtain a hyperspectral image and / or hyperspectral imaging data of, at least part of the wafer in a single shot or exposure.

[0126] The hyperspectral imaging camera may be arranged to obtain an image of the whole side or surface of the wafer, or part of the side or surface of the wafer. In the latter case, the hyperspectral imaging camera may be movable to image another part of the side or surface of the wafer, or one or more additional hyperspectral imaging cameras may be provided to image one or more other parts of the side or surface of the wafer.

[0127] The illumination source may comprise a broadband light source. For example, the broadband light source may comprise a broadband continuous light bulb, or a broadband pulsed light bulb, or a supercontinuum laser.

[0128] The hyperspectral imaging camera may perform the hyperspectral imaging and / or obtain the hyperspectral image and / or hyperspectral imaging data by imaging the broadband light reflected by the side or surface of the wafer.

[0129] The spectral imaging system may comprise a mechanism or arrangement or means for controllably selecting a specific wavelength or range or band of wavelengths to be detected by the detector.

[0130] The spectral imaging system may comprise a mechanism or arrangement or means for selectively changing a specific wavelength or specific range or specific band of wavelengths of illumination to be detected by the detector.

[0131] The spectral imaging system may comprise an imaging camera, for example a CCD camera, for obtaining an image of at least part of the wafer. As discussed above with regards to the hyperspectral camera, the imaging camera may be movable, or there may be a plurality of imaging cameras.

[0132] The spectral imaging system may be configured to obtain a plurality of different images of at least part of the wafer using the imaging camera for different specific wavelengths or specific ranges or specific bands of wavelengths of illumination.

[0133] The spectral imaging system or a processor or controller of the device may be configured to combine the data from the plurality of different images to obtain a spectral image or spectral imaging data. The illumination source may be operable to select a specific wavelength or specific range or specific band of wavelengths of illumination emitted by the illumination source.

[0134] The illumination source may be operable to selectively change a specific wavelength or specific range or specific band of wavelengths of illumination emitted by the illumination source.

[0135] The illumination source may comprise: a plurality of illumination sources each having a different wavelength or range or band of wavelengths, wherein the plurality of illumination sources are configured to be operated independently; or an illumination source having a tuneable or selectable wavelength or range of wavelengths of illumination.

[0136] For example, the plurality of illumination sources may be independently selected and operated so that the illumination source emits a specific wavelength or range or band of wavelengths.

[0137] The plurality of illumination source may comprise one or more of a multi-colour light source or multiple LEDs or multiple lasers with different emission wavelengths or ranges or bands of wavelength.

[0138] Alternatively, a light source, for example a broadband light source, may be used together with one or more filters for selectively transmitting a specific wavelength or range or band of wavelengths of the illumination.

[0139] For example, the filter may comprise a plurality of band pass filters, each of which is configured to transmit a different specific wavelength or range of wavelengths of illumination. The plurality of band pass filters may be independently arrangeable in a path of the illumination. For example, the plurality of band pass filters may be arranged on a wheel so that they can each be rotated into a path of the illumination.

[0140] Alternatively, the filter may comprise an adjustable or tuneable filter that is adjustable or tuneable to selectively transmit a specific wavelength or range of wavelengths of illumination. For example, the tuneable filter may be an acousto optical tuneable filter.

[0141] Alternatively, the filter may comprise a diffraction grating. The diffraction grating may be movable and / or rotatable in a path of the illumination to change a specific wavelength or range or band of wavelengths on the detector.

[0142] Alternatively, the filter may comprise a light dispersion device such as a prism. The light dispersion device may be movable and / or rotatable in a path of the illumination to change a specific wavelength or range or band of wavelengths on the detector.

[0143] The spectral imaging system may further comprise a reflector configured to reflect light from the illumination source onto the wafer, and the detector may be arranged to receive light reflected from the wafer. The reflector may be used instead of the optics mentioned above. Use of the reflector may serve to provide effective illumination of the side or surface of the wafer, so as to enable effective spectral imaging of the wafer.

[0144] The reflector may comprise any suitable reflective element for reflecting light from the illumination source onto the side or surface of the wafer. The spectral imaging system may comprise a support for supporting the wafer during spectral imaging of the wafer, with the reflector being configured (e.g. shaped, positioned, arranged) to reflect light from the illumination source onto the wafer when the wafer is on the support.

[0145] The detector may be arranged (e.g. positioned) so as to directly receive the light reflected from the side or surface of the wafer. For example, there may be no intervening optical components between the wafer and the detector.

[0146] The reflector may comprise a concave reflective surface arranged to reflect the light from the illumination source onto the wafer. Use of a concave reflective surface may facilitate providing even illumination across the side or surface of the wafer, enabling effective spectral imaging across the entire side or surface of the wafer. As an example, the concave reflective surface may be in the form of a reflective dome arranged over the wafer, i.e. over the support for supporting the wafer.

[0147] The concave reflective surface may be arranged such that a central (e.g. principal) axis of the concave reflective surface is substantially aligned with a centre (middle) of the wafer. For instance, the central axis of the concave reflective surface may be substantially aligned with a centre (middle) of the support of the spectral imaging system for supporting the wafer during spectral imaging of the wafer. Thus, the concave reflective surface may be arranged substantially symmetrically about the wafer and / or support. This facilitates even (uniform) illumination across the whole side or surface of the wafer.

[0148] An aperture may be formed in the reflector, and the detector may be arranged to receive light reflected from the wafer through the aperture in the reflector. In this manner, the detector may be arranged on an opposite side (e.g. on an outer side) of the reflector relative to the wafer. This may avoid the detector interfering with reflection of light by the reflector, to facilitate effective illumination of the wafer, as well as facilitate mounting the detector and making any required connections to the detector. This may also contribute to making the spectral imaging system more compact.

[0149] The aperture may be arranged and dimensioned so as to allow the detector to receive reflected light from all or part of the wafer. The aperture may correspond to a hole (through-hole) or opening in the reflector.

[0150] Where the reflector comprises the concave reflective surface mentioned above, the aperture may be formed in the concave reflective surface. For example, the aperture may be located at an apex of the concave reflective surface. Alternatively, the aperture may be offset from the apex of the concave reflective surface. Here, the apex of the concave reflective surface may refer to a position of the concave reflective surface on the central axis of the concave reflective surface.

[0151] The reflector may be configured to reflect the light from the illumination source as diffuse light. In other words, the reflector may be configured to diffuse incident light from the illumination source. Diffusing the light from the illumination source may contribute to providing more even (smooth) distribution of illumination across the whole wafer. For example, this may avoid or reduce peaks in illumination intensity at different regions on the wafer, thus improving reproducibility of spectral measurements across the whole wafer. As an example, the reflector may comprise a coating configured to diffuse light incident on the reflector. For instance, the concave reflective surface mentioned above may have a light-diffusing coating.

[0152] As noted above, the spectral imaging system may comprise a support for receiving (e.g. holding, supporting) the wafer during spectral imaging of the wafer. The illumination source may then comprise one or more light sources arranged around the support, with the reflector arranged to face towards the support and the one or more light sources. For example, the one or more light sources may be mounted adjacent to the support. In this manner, the reflector can reflect light from the one or more light sources back towards the support (and hence the wafer). Arranging the one or more light sources around the support may contribute to making the spectral imaging system more compact, as the light sources can be directly integrated into the spectral imaging system, without having to provide optics for coupling in light from an external light source. Furthermore, such an arrangement may contribute to providing an even illumination across the wafer.

[0153] In some cases, the illumination source may comprise a plurality of light sources arranged (e.g. in a ring) around the support. In this manner, light from the plurality of light sources may be reflected onto the wafer, enabling effective illumination of the side or surface of the wafer. The plurality of light sources may be evenly spaced around the support.

[0154] Where the reflector comprises a concave reflective surface, the one or more light sources may be angled (e.g. inclined, oriented) towards the central axis of the concave reflective surface. In other words, light from the one or more light sources may be directed inwards, towards the central axis or apex of the concave reflective surface. As a result, an angle of incidence of light on the side or surface of the wafer may be relatively low, which may facilitate spectral imaging of the wafer.

[0155] The metrology apparatus may be configured to determine a dimension of the wafer at a plurality of locations on the wafer based on the output of the spectral imaging system and a learned model. For example, the metrology apparatus may comprise a processor or controller for determining the dimension. The dimension is a dimension of interest, for example a thickness of a layer of film or material on the side or surface of the wafer, or a critical dimension, or a side wall angle, or an etch hole diameter, for example. In general, the dimension may be a dimension of a layer or pattern of interest on the wafer.

[0156] The metrology apparatus, for example a processor or controller of the metrology apparatus, may be further configured to generate a spatial distribution model of the dimension for the side or surface of the wafer based on at least the determined dimension at the plurality of locations.

[0157] The metrology apparatus may be configured to generate the spatial distribution model of the dimension for the side or surface of the wafer based on the determined dimensions at the plurality of locations and the mass and / or change in mass for the wafer measured by the mass metrology station.

[0158] The metrology apparatus, for example a processor or controller of the metrology apparatus, may be configured to determine information regarding a bow or curvature of the wafer from the output of the spectral imaging system. The metrology apparatus, for example a processor or controller of the metrology apparatus, may be configured to: obtain a plurality of images at different wavelengths or ranges of wavelengths using the spectral imaging system; analyse a defocus pattern in each of the plurality of images; and determine information regarding a bow or curvature of the wafer from the results of the analysis.

[0159] According to a second aspect of the present invention there is provided a metrology apparatus comprising an imaging system for performing imaging of at least part of a wafer, wherein the metrology apparatus is configured to determine information regarding a bow or curvature of the wafer from the output of the imaging system.

[0160] The imaging system may be a spectral imaging system, for example an optical spectral imaging system.

[0161] The metrology apparatus, for example a processor or controller of the metrology apparatus, may be configured to: obtain an image using the imaging system, analyse a defocus pattern in the image; and determine information regarding a bow or curvature of the wafer from the results of the analysis.

[0162] The metrology apparatus, for example a processor or controller of the metrology apparatus, may be configured to: obtain a plurality of images at different wavelengths or ranges of wavelengths using the imaging system; analyse a defocus pattern in each of the plurality of images; and determine information regarding a bow or curvature of the wafer from the results of the analysis.

[0163] Where the imaging system is a spectral imaging system, the processor may be configured to use spectral imaging data for one or a sub-set of different wavelengths or ranges of wavelengths for determining the information regarding the bow or curvature of the wafer. In particular, it is not essential for the processor to use all of the spectral imaging data for determining the information regarding the bow or curvature of the wafer, and instead this information may be determined using only some or a sub-set of the spectral imaging data. In particular, the processor may use one or a subset of channels (i.e. wavelengths or ranges of wavelengths) of the spectral imaging data for determining the information regarding the bow or curvature of the wafer.

[0164] The metrology apparatus according to the second aspect of the present invention may have any of the features of the first aspect of the present invention, unless incompatible.

[0165] The metrology apparatus of either aspect may be configured to perform optical interferometry between the wafer and a reference wafer.

[0166] The metrology apparatus of either aspect may comprise a reference unit comprising a reference wafer, and the spectral imaging system may be configured to perform optical interferometry between the wafer and the reference wafer.

[0167] According to a third aspect of the present invention there is provided a metrology apparatus comprising a spectral imaging system for performing spectral imaging of at least part of a wafer, wherein the metrology apparatus is configured to perform optical interferometry between the wafer and a reference wafer. The metrology apparatus may comprise a reference unit comprising a reference wafer, and the spectral imaging system may be configured to perform optical interferometry between the wafer and the reference wafer.

[0168] When performing the optical interferometry, it is not necessary to use all of the spectral imaging data. Instead, the metrology apparatus may be configured to use one or a sub-set of channels of the spectral imaging data.

[0169] The invention includes the combination of the aspects and preferred features described except where such a combination is clearly impermissible or expressly avoided.

[0170] Summary of the Figures

[0171] Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which:

[0172] Figure 1 is a schematic illustration of a mass metrology apparatus.

[0173] Figure 2 is a schematic illustration of a metrology apparatus according to a first embodiment of the present invention.

[0174] Figure 3 is a schematic illustration of a metrology apparatus according to a second embodiment of the present invention.

[0175] Figure 4 is a schematic illustration of a metrology apparatus according to a third embodiment of the present invention.

[0176] Figure 5 is a schematic illustration of a metrology apparatus according to a fourth embodiment of the present invention.

[0177] Figure 6 is a schematic illustration of a metrology apparatus according to an embodiment of the present invention.

[0178] Figure 7 is a schematic illustration of a metrology apparatus according to an embodiment of the present invention. Figure 8 is a schematic illustration of part of a metrology apparatus according to an embodiment of the present invention.

[0179] Figure 9 illustrates an example analysis of hyperspectral imaging data in an embodiment of the present invention.

[0180] Figure 10 is a schematic illustration of a metrology apparatus according to an embodiment of the present invention.

[0181] Figure 11 illustrates an example of measurement data obtained using the metrology apparatus of Figure 10.

[0182] Figure 12 is a schematic illustration of part of a metrology apparatus according to an embodiment of the present invention.

[0183] Detailed Description of the Invention

[0184] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference.

[0185] Figure 1 is a schematic illustration of a mass metrology apparatus 1 for measuring the mass and / or the change in mass of a wafer, such as a semiconductor wafer. The mass metrology apparatus 1 comprises a first thermalisation station 3, a second thermalisation station 5 and a mass metrology station 7.

[0186] The mass metrology station 7 is configured to measure the mass and / or the change in mass of a wafer. The mass metrology station 7 comprises a measurement chamber 9 and a device 11 that is housed in the measurement chamber 9. The device 11 is configured to measure the weight or mass, and / or the change in weight or mass, of a wafer loaded onto the device 11 .

[0187] The device 11 comprises a load cell 13 and a pan or support 15 that is coupled to the load cell 13 and that is configured to support a wafer during a measurement by the device 11 .

[0188] The measurement chamber 9 may form an enclosed environment around the device 11 . For example, the measurement chamber 9 may maintain a substantially uniform air density, air pressure and air temperature of the air around the device 11 . The measurement chamber 9 may have an opening (not shown), e.g. a suitably sized slot in a side-wall of the measurement chamber 9, to allow a wafer to be transported into the measurement chamber 9, for example by an end effector of a robotic arm, and positioned on the pan 15 of the device 11. When not in use, the opening may be covered by an openable door or covering (not shown) to allow the measurement chamber 9 to be substantially closed or sealed when performing measurements using the device 11 .

[0189] Of course, the configuration of the mass metrology station 7, and / or measurement chamber 9 and / or device 11 may be different to that illustrated in Figure 1 .

[0190] The first thermalisation station 3 and second thermalisation station 5 are for changing the temperature of the wafer before the wafer is loaded into the mass metrology station 7. Specifically, in operation the wafer is sequentially loaded into the first thermalisation station 3 and then the second thermalisation station 5 before being loaded into the mass metrology station 7. Therefore, the temperature of the wafer is changed by both the first thermalisation station 3 and the second thermalisation station 5 before the wafer is loaded into the mass metrology station 7.

[0191] Of course, in other embodiments only a single thermalisation station, for example only the first thermalisation station 3 or the second thermalisation station 5, may be included in the mass metrology apparatus 1 .

[0192] If the temperature of the wafer is different to a temperature of the mass metrology station 7 when the wafer is place / moved into the mass metrology station 7, this may negatively affect the accuracy of the mass measurement. For example, if the temperature of the wafer is different to a temperature of the measurement chamber 9, the temperature of the wafer may cause convection currents to occur in the air inside the measurement chamber 9 once the wafer is inserted into the measurement chamber 9, which may negatively affect the accuracy of the mass measurement. Alternatively, or in addition, if the temperature of the wafer is different to a temperature of the measurement chamber 9, this may cause a change in the temperature of the air inside the measurement chamber 9 once the wafer is placed / moved into the measurement chamber 9, which may change the buoyancy force on the wafer. This may negatively affect the accuracy of the mass measurement.

[0193] Therefore, the first thermalisation station 3 and second thermalisation station 5 may be configured to change the temperature of the wafer to be equal to, or within a predetermined temperature of, a temperature of the mass metrology station 7, for example to be equal to, or within a predetermined temperature of, a temperature of the measurement chamber 9. For example, the first thermalisation station 3 and second thermalisation station 5 may be configured to change the temperature of the wafer to be within ±0.1 °C of the temperature of the mass metrology station 7 or measurement chamber 9.

[0194] The first thermalisation station 3 is configured to cause a bulk of the total change in the temperature of the wafer that is caused by the first and second thermalisation stations 3 and 5, and the second thermalisation station 5 is configured to cause a smaller change in the temperature of the wafer than the first thermalisation station 3.

[0195] In this embodiment the first thermalisation station 3 and second thermalisation station 5 may be for cooling the wafer, since the temperature of the wafer when it arrives at the mass metrology apparatus 1 after processing of the wafer is typically higher than a temperature of the mass metrology station 7 or measurement chamber 9. Of course, the first thermalisation station 3 and / or the second thermalisation station 5 may instead be for heating a wafer, where the temperature of the wafer is less than a temperature of the mass metrology station 7 or measurement chamber 9.

[0196] The first thermalisation station 3 is configured to actively change the temperature of the wafer, for example to actively cool the wafer. In particular, the first thermalisation station 3 may use one or more powered heating or cooling devices, for example one or more thermoelectric devices, to increase or reduce the temperature of the wafer. The first thermalisation station 3 may actively dissipate heat from the wafer, for example into an air flow through or adjacent to the first thermalisation station 3, when cooling a wafer.

[0197] The first thermalisation station 3 comprises a first temperature changing part 17 on which the wafer can be positioned and that is configured to change the temperature of the wafer (for example cool the wafer or heat the wafer). For example, the first temperature changing part 17 may comprise a plate or block. The plate or block may be made of, or comprise, one or more materials having a good thermal conductivity (for example Al).

[0198] The first temperature changing part 17 may further comprise a plurality of Peltier devices attached on a bottom side of the plate or block (or another part of the plate or block), and / or in contact with the bottom side of the plate or block (or another part of the plate or block). The Peltier devices may be operable to actively dissipate heat from the plate or block, for example into an air flow, when cooling a wafer. For example, the Peltier devices may be operable to control the temperature of the plate or block to be a predetermined temperature.

[0199] The first thermalisation station 3 may comprise a chamber that encloses or partly encloses the first temperature changing part 17, wherein the chamber has an opening through which a wafer can be inserted and positioned on the first temperature changing part 17, for example by an end effector of a robotic arm.

[0200] The second thermalisation station 5 is configured to passively change the temperature of the wafer, for example to passively cool the wafer. In particular, the second thermalisation station 5 comprises a second temperature changing part 19 that is positioned on top of the measurement chamber 9. The second temperature changing part 19 may comprise a plate or block. The plate or block may be made of, or comprise, one or more materials having a good thermal conductivity, for example Al.

[0201] The second temperature changing part 19 preferably has a high thermal mass, so that its temperature changes slowly and little when it is supplied with heat, and / or a good lateral thermal conductivity, so that it maintains a substantially uniform temperature across its upper surface.

[0202] The second thermalisation station 7 may comprise a chamber that encloses or partly encloses the second temperature changing part 19, wherein the chamber has an opening through which a wafer can be inserted and positioned on the second temperature changing part 19, for example by an end effector of a robotic arm.

[0203] The second temperature changing part 19 is positioned directly on top of the measurement chamber 9, so that there is a good thermal contact between the second temperature changing part 19 and the measurement chamber 9. The second temperature changing part 19 is in direct physical contact with the measurement chamber 9. For example, the second temperature changing part 19 may be attached or fixed to the measurement chamber 9, for example using one or more bolts (not shown) and / or a thermally conductive bonding layer (not shown).

[0204] As a result of the good thermal contact between the second temperature changing part 19 and the measurement chamber 9, the second temperature changing part 19 may be substantially in thermal equilibrium with the measurement chamber 9 and therefore may have substantially the same temperature as the measurement chamber 9 (when a heat load on the second temperature changing part 19 is low). Therefore, when a wafer is loaded onto the second temperature changing part 19, the wafer may be brought into thermal equilibrium with the measurement chamber 9, so that the wafer has substantially the same temperature as the measurement chamber 9.

[0205] As shown in Figure 1 , the mass metrology apparatus 1 further comprises a wafer handling system 2 for loading a wafer into each of the first thermalisation station 3, the second thermalisation station 5 and the mass metrology station 7, and for removing a wafer from each of these stations. For example, the wafer handling system 2 may comprise one or more robotic arms 4, each having one or more end effectors 6 for supporting and / or carrying a wafer. Of course, the configuration of the wafer handling system may be different to that illustrated in Figure 1 . Although shown separately in Figure 1 , the wafer handling system is typically integral to the apparatus 1 .

[0206] As shown in Figure 1 , the first thermalisation station 3, second thermalisation station 5 and mass metrology station 7 are integrated into a single apparatus. In other words, the first thermalisation station 3, second thermalisation station 5 and mass metrology station 7 are all connected together, and / or fixed together, and / or mounted on one another in a stack.

[0207] Of course, in other embodiments the relative positions of the first thermalisation station 3, second thermalisation station 5 and mass metrology station 7 may be different to that illustrated in Figure 1 . For example, the order of each of the stations in the stack may be different, and / or one or more of the stations may be positioned to the side of one of the other stations instead of on top of, or beneath, one of the other stations.

[0208] Figure 2 is a schematic illustration of a metrology apparatus 21 according to a first embodiment of the present invention.

[0209] The metrology apparatus 21 may be a modified version of the mass metrology apparatus 1 illustrated in Figure 1 . The metrology apparatus 21 may therefore have any of the features of the mass metrology apparatus 1 illustrated in Figure 1 or described above, unless incompatible with the features descried below.

[0210] Some features of the metrology apparatus 21 that are the same as the features of the mass metrology apparatus 1 illustrated in Figure 1 are indicated using the same reference numbers in Figure 2, and description thereof is not repeated for conciseness. The metrology apparatus 21 according to the first embodiment of the present invention differs from the mass metrology apparatus 1 of Figure 1 in that the metrology apparatus 21 further includes a hyperspectral imaging system 23.

[0211] As shown in Figure 2, in this embodiment the hyperspectral imaging system 23 is integrated with (or into) the first thermalisation station 3, so that the hyperspectral imaging system 23 is configured to perform hyperspectral imaging of a wafer 25 while the wafer is loaded onto the first temperature changing part 17 of the first thermalisation station 3.

[0212] In Figure 2 all the components of the hyperspectral imaging system 23 are illustrated as being inside the first thermalisation station 3. However, one, some or all of the components may be located outside of the first thermalisation station 3.

[0213] In this embodiment the hyperspectral imaging system 23 comprises a hyperspectral imaging camera 26 that is configured to perform hyperspectral imaging of, or obtain a hyperspectral image of, or obtain hyperspectral imaging data of, a side or surface of the wafer. In addition, the hyperspectral imaging system 23 further comprises an illumination source 27, for example a light source such as broadband light source, that is configured to configured to generate illumination such as light for performing the hyperspectral imaging of, or obtaining the hyperspectral image of, or obtaining the hyperspectral imaging data of the side or surface of the wafer.

[0214] The hyperspectral imaging camera 26 may comprise a snapshot camera or a pushbroom camera, for example.

[0215] Furthermore, the hyperspectral imaging system 23 further comprises optics 29 that is configured to guide or direct the illumination generated by the illumination source 27 onto a wafer that is loaded onto the first temperature changing part 17 and to direct reflected illumination (for example reflected light) from the wafer to the hyperspectral imaging camera 26 for performing the hyperspectral imaging and / or obtaining the hyperspectral image or hyperspectral imaging data. For example, as discussed below, the optics 29 may comprise one or more of a beam splitter and one or more lenses, such as convex lenses.

[0216] Of course, the arrangement of the illumination source 27, optics 29 and camera 26 may be different to that illustrated schematically in Figure 2.

[0217] Therefore, in this embodiment, hyperspectral imaging of the wafer can be performed while the wafer is positioned on the first temperature changing part 17 in the first thermalisation station 3 and having its temperature changed by the first temperature changing part 17. Therefore, a hyperspectral image and / or hyperspectral imaging data of the wafer 25 can be obtained while the wafer is positioned on the first temperature changing part 17.

[0218] The hyperspectral imaging data may correspond to, or illustrate, or measure, a spectroscopic reflectance (for example an optical spectroscopic reflectance) of the side or surface of the wafer, for example at all areas of the side or surface of the wafer, or at all areas of part of the side or surface of the wafer. The hyperspectral imaging data may comprise spectral data, for example optical spectral data, for all areas of the side or surface of the wafer, or for all areas of part of the side or surface of the wafer.

[0219] The hyperspectral imaging data may comprise or include optical spectral data.

[0220] The hyperspectral imaging data may comprise a hyperspectral data cube for some or all of the side or surface of the wafer.

[0221] The hyperspectral image or hyperspectral imaging data may be an image comprising spectral data (for example optical spectral data) for each pixel of the image.

[0222] The hyperspectral image or hyperspectral imaging data may be an image comprising an optical spectrum for each pixel of the image.

[0223] The hyperspectral image or hyperspectral imaging data may be a single image comprising intensity versus wavelength data for each pixel of the image.

[0224] Alternatively, the hyperspectral image or hyperspectral imaging data may comprise a plurality of images, each corresponding to a different wavelength or range or band of wavelengths of illumination and each comprising intensity data for each pixel of the image.

[0225] As discussed above, combining the hyperspectral imaging of the wafer and the thermalisation of the wafer in this manner can provide a number of advantages over performing both steps separately. For example, a total footprint and cost of the metrology apparatus may be reduced, and a total metrology time for the wafer in the metrology apparatus may be reduced.

[0226] Furthermore, as discussed above, since the hyperspectral imaging system 23 has minimal moving parts (as compared to some other types of optical metrology systems) and therefore causes minimal vibration, the hyperspectral imaging system 23 may not negatively affect any measurement being performed by the mass metrology station 7 on a first wafer at the same time that hyperspectral imaging is being performed by the hyperspectral imaging system 23 on a second wafer.

[0227] In addition, since the hyperspectral imaging system 23 has minimal moving parts (as compared to some other types of optical metrology systems), the hyperspectral imaging system 23 may cause reduced electromagnetic noise, and may therefore not negatively affect any measurement being performed by the mass metrology station 7 on a first wafer at the same time that hyperspectral imaging is being performed by the hyperspectral imaging system 23 on a second wafer.

[0228] The metrology apparatus 21 further comprises a processor 31 or controller that is configured to receive hyperspectral imaging data from the hyperspectral imaging system 23 and mass metrology data (mass and / or change in mass) from the mass metrology station 7.

[0229] The processor 31 may be configured to assess one or more parameters of the wafer based on one or both of the hyperspectral imaging data and the mass metrology data (mass and / or change in mass). For example, the processor may be configured to determine uniformity data about the side or surface of the wafer based on the hyperspectral imaging data, or based on both the hyperspectral imaging data and the mass metrology data (mass and / or change in mass). The uniformity data may relate to the uniformity of one or more of a thickness of a layer on the side or surface of the wafer, or a critical dimension of a pattern on the side or surface of the wafer, for example. The uniformity data may relate to the uniformity of a pattern of interest across the wafer. The uniformity data may relate to a specific dimension of the wafer.

[0230] Combining the mass metrology data (mass and / or change in mass) with the hyperspectral imaging data may improve the reliability and sensitivity of the determination of the uniformity data relative to using the hyperspectral imaging data alone. Alternatively, or in addition, combining the hyperspectral imaging data with the mass metrology data (mass and / or change in mass) may provide uniformity information that is not provided by the mass metrology data alone. The hyperspectral imaging data and mass metrology data may therefore be combined synergistically to improve the assessment of one or more parameters of the wafer.

[0231] The hyperspectral imaging system 23 may be configured to perform hyperspectral imaging and / or obtain a hyperspectral image or hyperspectral imaging data of the whole side or surface of the wafer 25. Alternatively, the hyperspectral imaging system 23 may be configured to perform hyperspectral imaging and / or obtain a hyperspectral image or hyperspectral imaging data of part of the side or surface of the wafer. In that case, a plurality of different hyperspectral imaging systems 23, or a hyperspectral imaging system 23 having a plurality of different hyperspectral imaging cameras 26, may be used to obtain different hyperspectral images or hyperspectral imaging data of different parts of the wafer. Alternatively, part of the hyperspectral imaging system 23, for example the optics 29 and / or the hyperspectral imaging camera 26, may be movable (for example translatable parallel to the side or surface of the wafer) to obtain hyperspectral images or hyperspectral imaging data of different parts of the side or surface of the wafer. Alternatively, the wafer or a support that is supporting the wafer may be movable (for example translatable parallel to the side or surface of the wafer) to obtain hyperspectral images or hyperspectral imaging data of different parts of the side or surface of the wafer.

[0232] The hyperspectral imaging data may be used to determine or measure uniformity of the side or surface of the wafer, for example the uniformity of a pattern of interest across the side or surface of the wafer.

[0233] The processor 31 may be configured to perform the following steps using the hyperspectral imaging data: (i) identify one or multiple locations of interest on the side or surface of the wafer; (ii) extract optical spectral information (or spectra) from each location of interest; and (iii) analyse the extracted optical spectral information (or spectra) to obtain wafer uniformity information.

[0234] The extracted spectral information (or spectra) may be combined with the mass metrology data (mass and / or change in mass) for the wafer to produce more reliable and accurate analysis of the wafer, for example to enable more accurate and reliable wafer to wafer uniformity comparison, or within wafer uniformity comparison.

[0235] Figure 3 is a schematic illustration of a metrology apparatus 33 according to a second embodiment of the present invention. In the second embodiment, the hyperspectral imaging system 23 is integrated with (or into) the second thermalisation station 5 instead of the first thermalisation station 3, so that the hyperspectral imaging system 23 is configured to perform hyperspectral imaging of a wafer 25 while the wafer is loaded onto the second temperature changing part 19 of the second thermalisation station 5.

[0236] In Figure 3 all the components of the hyperspectral imaging system 23 are illustrated as being inside the second thermalisation station 5. However, one, some or all of the components may be located outside of the second thermalisation station 5.

[0237] Otherwise, the features and operation of the metrology apparatus 33 according to the second embodiment may be the same as the features of the metrology apparatus 21 according to the first embodiment, unless incompatible.

[0238] The features of Figure 3 that are the same as, or correspond to, the features of Figures 1 and 2 are indicated with the same reference signs in Figure 3, and description thereof is not repeated here for conciseness.

[0239] Figure 4 is a schematic illustration of a metrology apparatus 35 according to a third embodiment of the present invention. In the third embodiment the hyperspectral imaging system 23 is integrated with (or into) the mass metrology station 7 instead of the first or second thermalisation station 3 or 5, so that the hyperspectral imaging system 23 is configured to perform hyperspectral imaging of a wafer 25 while the wafer is loaded onto the pan 15 of the device 11 in the mass metrology station 7.

[0240] In Figure 4 all the components of the hyperspectral imaging system 23 are illustrated as being inside the mass metrology station 7. However, one, some or all of the components may be located outside of the mass metrology station 7.

[0241] Otherwise, the features and operation of the metrology apparatus 35 according to the third embodiment may be the same as the features of the metrology apparatus 21 according to the first embodiment, unless incompatible.

[0242] The features of Figure 4 that are the same as, or correspond to, the features of Figures 1 , 2 and 3 are indicated with the same reference signs in Figure 4, and description thereof is not repeated here for conciseness.

[0243] In the embodiment of Figure 4, the device 11 may be controlled not to perform a measurement while the hyperspectral imaging system 23 is performing hyperspectral imaging, to avoid the operation of the hyperspectral imaging system 23 from affecting the accuracy of the measurement by the device 11 .

[0244] Figure 5 is a schematic illustration of a metrology apparatus 37 according to a fourth embodiment of the present invention. In the fourth embodiment the hyperspectral imaging system 23 is included in a hyperspectral imaging station 39, instead of being integrated into one of the other stations 3, 5 or 7. The hyperspectral imaging station 39 is separate to the first thermalisation station 3, second thermalisation station 5 and mass metrology station 7.

[0245] The first thermalisation station 3, second thermalisation station 5, mass metrology station 7 and hyperspectral imaging station 39 are all integrated into a single apparatus. For example, the first thermalisation station 3, second thermalisation station 5, mass metrology station 7 and hyperspectral imaging station 39 are all connected together, and / or fixed together, and / or mounted on one another in a stack.

[0246] In the fourth embodiment, the wafer handling system 2 is further configured to load a wafer into the hyperspectral imaging station 39, and to remove a wafer from the hyperspectral imaging station 39. Therefore, a single wafer handling system 2 is used to load and unload a wafer into each of the first thermalisation station 3, second thermalisation station 5, mass metrology station 7 and hyperspectral imaging station 39.

[0247] In the fourth embodiment the hyperspectral imaging station 39 is positioned on top of the first thermalisation station 3. Of course, in other embodiments the hyperspectral imaging station 39 may be differently positioned.

[0248] In this embodiment, the hyperspectral imaging station 39 is separate to the first thermalisation station 3, second thermalisation station 5 and mass metrology station 7, but is connected to at least one of the first thermalisation station 3, second thermalisation station 5 and mass metrology station 7.

[0249] The hyperspectral imaging station 39 comprises a support, for example a chuck, for supporting the wafer during the hyperspectral imaging.

[0250] In addition, the hyperspectral imaging station 39 may comprise a housing or chamber for enclosing the wafer during the hyperspectral imaging, the housing or chamber may have an opening for inserting and removing a wafer into the hyperspectral imaging station 39.

[0251] In operation of the metrology apparatus 33, a wafer is sequentially moved between the hyperspectral imaging station 39, the first thermalisation station 3, the second thermalisation station 5, and the mass metrology station 7. Therefore, a hyperspectral image or hyperspectral imaging data of the wafer is generated before thermalisation of the wafer and mass metrology of the wafer. Alternatively, the wafer may be moved to the hyperspectral imaging station 39 after the mass metrology station 5.

[0252] Figure 6 is a schematic illustration of a metrology apparatus 41 according to an embodiment of the present invention.

[0253] Figure 6 may be a partial view of the system 33 of the second embodiment illustrated in Figure 3, in which the hyperspectral imaging system 23 is integrated with (or into) the second thermalisation station 5. The embodiment of Figure 6 may therefore include any of the features of the second embodiment, unless incompatible, and the second embodiment may include any of the features of Figure 6 unless incompatible. Alternatively, the embodiment of Figure 6 may be a separate embodiment without the additional features of the second embodiment.

[0254] Features of Figure 6 that are the same as, or correspond to, features of the previous embodiments discussed above are illustrated with the same reference signs in Figure 6, and description thereof is not repeated here for conciseness. As for the second embodiment illustrated in Figure 3, the hyperspectral imaging system 23 is configured to perform hyperspectral imaging of a wafer 25 while the wafer is loaded onto a temperature changing part 19 of a thermalisation station.

[0255] The optics 29 of the hyperspectral imaging system 23 are configured to direct the illumination generated by the illumination source 27 onto the wafer 25 that is loaded onto the temperature changing part 19 and to direct reflected illumination from the wafer 25 to the hyperspectral imaging camera 26 for performing the hyperspectral imaging and / or obtaining the hyperspectral image or hyperspectral imaging data.

[0256] In this embodiment, the optics 29 comprise a beam splitter 43 that directs light from the illumination source 27 towards the wafer 25, and that transmits light from the wafer 25 towards the hyperspectral imaging camera 26.

[0257] Furthermore, the optics 29 further comprise a plurality of lenses 45a, 45b and 45c for illuminating the light generated by the illumination source 27 onto the wafer 25 and for directing light from the wafer to the hyperspectral imaging camera 26 for performing the hyperspectral imaging and / or obtaining the hyperspectral image or hyperspectral imaging data, in combination with the beam splitter 43.

[0258] For example, the plurality of lenses may comprise a first lens 45a positioned on an optical path from the illumination source 27 to the beam splitter 43, a second lens 45b positioned on an optical path between the beam splitter 43 and the wafer 25, and a third lens 45c positioned on an optical path between the beam splitter 43 and the hyperspectral imaging camera 26.

[0259] In addition, in this embodiment the optics 29 further comprises an optional polariser 47 on an optical path from the beam splitter 43 to the hyperspectral imaging camera 26, for example between the third lens 45c and the hyperspectral imaging camera 26. Of course, if included, the polariser 47 may be located in a different position relative to the other components of the optics 29.

[0260] Of course, this is merely an example of suitable optics 29, and other configurations of the optics 29 are possible for achieving the same or similar effects and may be used instead of the optics 29 described above. The specific configuration or arrangement of the optics 29 is not essential to the present invention.

[0261] In this embodiment, the illumination source 27 is a broadband light source. For example, the illumination source 27 may be configured to emit light having a wide range of wavelengths simultaneously. The illumination source 27 may include a polariser. The broadband light source may be a broadband continuous light bulb, or a broadband pulsed light bulb, or a supercontinuum laser, for example.

[0262] In Figure 6 the hyperspectral imaging system 23 is illustrated as obtaining a hyperspectral image or hyperspectral imaging data of the whole of the upper side or surface of the wafer 25. In an alternative arrangement, the hyperspectral imaging system 23 may instead be configured to obtain an image of only part of the upper side or surface of the wafer. One or more parts of the hyperspectral imaging system 23 may be movable or adjustable to change an area of the upper side or surface of the wafer that is being imaged. Alternatively, the hyperspectral imaging system 23 may comprise a plurality of hyperspectral imaging cameras 26 that are arranged to obtain images of different parts of the side or surface of the wafer 25.

[0263] Figure 7 is a schematic illustration of a metrology apparatus 49 according to an embodiment of the present invention. The metrology apparatus 49 is a modified version of the metrology apparatus 41 of Figure 6.

[0264] Features of Figure 7 that are the same as, or correspond to, features of the previous embodiments discussed above are illustrated with the same refence signs in Figure 7, and description thereof is not repeated here for conciseness.

[0265] In the embodiment of Figure 7, an imaging camera such as a charge-coupled device (CCD) camera 51 is used instead of the hyperspectral imaging camera 26. In this embodiment, a hyperspectral image or hyperspectral imaging data of the wafer is obtained using the CCD camera 51 by selecting different wavelengths to be imaged by the CCD camera 51 , either by selecting different wavelengths to be emitted by the illumination source 53, or by selecting different wavelengths to be input to the CCD camera 51 .

[0266] For example, the illumination source 53 may be controllable to selectively emit light having a specific wavelength or range or band of wavelengths. For example, the illumination source 53 may comprise a plurality of different illumination sources that is each configured to emit light having a different specific wavelength or range or band of wavelengths, wherein each of the plurality of different illumination sources can be selectively activated to selectively emit light having the respective wavelength or range or band of wavelengths. For example, the plurality of illumination sources may comprise a plurality of LEDs having different wavelengths, or a plurality of lasers having different wavelengths.

[0267] Alternatively, the illumination source 53 may be a single illumination source that is adjustable or tuneable to adjust or select a wavelength or range or band or wavelengths of light emitted by the illumination source. In other words, the illumination source 53 may be tuneable to a specific wavelength or range or band of wavelengths. For example, the illumination source may be a tuneable laser.

[0268] In this manner, a hyperspectral image or hyperspectral imaging data of the wafer may be obtained by taking a series of images using the CCD camera 51 for different wavelengths of light emitted by the illumination source 53.

[0269] Alternatively, the illumination source 53 may be a broadband light source as discussed above, and the hyperspectral imaging system 23 may comprise a wavelength selecting device for selecting a specific wavelength or range or band of wavelengths from the light emitted by the broadband light source to be used to perform the spectral imaging.

[0270] For example, the hyperspectral imaging system 23 may comprise a bandpass filter. For example, the hyperspectral imaging system 23 may comprise a tuneable or adjustable bandpass filter. The bandpass filter may be positioned on an optical path from the illumination source adjacent to the illumination source, for example. Alternatively, the bandpass filter may be positioned elsewhere on the optical path from the illumination source to the CCD camera 51 . Therefore, the wavelength selecting device, for example bandpass filter, may be adjusted or tuned to select a specific wavelength or range or band of wavelengths to be imaged using the CCD camera 51 .

[0271] An example of a suitable wavelength selecting device may be a bandpass filter wheel, which comprises a plurality of different bandpass filters that selectively transmit light having different specific wavelengths or ranges or bands of wavelengths, wherein the bandpass filter wheel can be rotated to position different ones of the bandpass filters in the optical path.

[0272] Another example of a suitable wavelength selecting device may be a tuneable filter, for example an acousto-optic tuneable filter.

[0273] Another example of a suitable wavelength selecting device may be a diffraction grating, for example which may be movable and / or rotatable to vary a selected wavelength or range or band of wavelengths that are imaged by the CCD camera 51 .

[0274] Another example of a suitable wavelength selecting device may be a light dispersion device, for example a prism, for example which may be movable and / or rotatable to vary a selected wavelength or range or band of wavelengths that are imaged by the CCD camera 51 .

[0275] One embodiment may use a super continuum laser as the light source in combination with an acousto- optic tuneable filter at the illumination side and a high resolution CCD camera as the detector. Such a configuration may be capable of measuring a high-resolution image with high resolution broadband spectrum with a high signal-to-noise ratio and at high speed.

[0276] Figure 8 is a schematic illustration of part of a metrology apparatus according to an embodiment of the present invention.

[0277] In particular, the arrangement illustrated in Figure 8 may be used as, or included in, the hyperspectral imaging station 39 in Figure 5. The embodiment of Figure 8 may therefore include any of the features of the fourth embodiment, unless incompatible, and the fourth embodiment may include any of the features of Figure 8 unless incompatible.

[0278] Specifically, Figure 8 illustrates a configuration of the hyperspectral imaging system 23 in the hyperspectral imaging station 39 in Figure 5. The hyperspectral imaging system 23 may have any of the features of any of the hyperspectral imaging systems 23 discussed above, unless incompatible.

[0279] In addition, the hyperspectral imaging system 23 further includes a support 55 for supporting the wafer during hyperspectral imaging of the wafer 25. For example, the support 55 may comprise a chuck or a plate or block.

[0280] In this embodiment, the support 55 is merely for supporting the wafer 25 during the hyperspectral imaging, and is not configured to cause a predetermined change in the temperature of the wafer 25.

[0281] Therefore, the hyperspectral imaging system 23 is not integrated with (or into) a thermalisation station or mass measurement station. Of course, the different embodiments described above can be combined together in different ways. For example, the hyperspectral imaging system 23 of either Figure 6 or Figure 7 can be used in any of the first to fourth embodiments described above.

[0282] In addition, it is not essential to include two different thermalisation stations as illustrated in the figures. Instead, only a single thermalisation station may be included, which may be either an active or a passive thermalisation station, for example, and which may correspond to either the first thermalisation station 3 or the second thermalisation station 5 in Figure 1. In some embodiments, the apparatus may not include any thermalisation stations, and instead the hyperspectral imaging system may be integrated with (or into) the mass metrology station 7, or may be provided as a separate hyperspectral imaging station 39 that is attached to, or fixed to, or mounted on, the mass metrology station 7.

[0283] It is also not essential for the stations to be mounted one on top of another in a stack as illustrated in the figures. Instead, in other embodiments one or more of the stations may be positioned side by side, for example.

[0284] As mentioned above, the hyperspectral imaging data obtained by the hyperspectral imaging system 23 in any of the embodiments of the present invention may be processed or used to assess one or more parameters of the wafer, for example the uniformity of the side or surface of the wafer, for example uniformity of a dimension or pattern of interest across the side or surface of the wafer.

[0285] Using the system of Figure 6 for example, the hyperspectral imaging data may include optical spectral data for every pixel of a whole field image of the wafer or a partial image of the wafer.

[0286] An image processing algorithm or image processing algorithms may be used to select optical spectra data from points or areas of interest on the wafer from the hyperspectral imaging data.

[0287] The selected optical spectra data may then be analysed to obtain wafer uniformity information, for example to generate a wafer uniformity map for the side or surface of the wafer.

[0288] Alternatively, using the system of Figure 7 for example, the hyperspectral imaging data may comprise a plurality of images of the wafer obtained for different selected wavelengths or ranges or bands of wavelengths of illumination.

[0289] The processing of the hyperspectral imaging data may comprise using an image processing algorithm or image processing algorithms to extract intensity data from points or areas of interest on the wafer from each of the plurality of images (corresponding to different wavelengths of illumination), and combining the intensity data for each of the points or areas of interest to generate optical spectral data for the point or area of interest.

[0290] As above, the obtained optical spectra data may then be analysed to obtain wafer uniformity information, for example a wafer uniformity map for the side or surface of the wafer.

[0291] In either case, mass metrology data (mass and / or change in mass) obtained for the wafer may be combined with the optical spectral data to obtain the wafer uniformity information.

[0292] The processing may be performed by the processor 31 . The metrology apparatus (for example the processor 31) may comprise a modelling module that generates a dimension of interest at the plurality of points or areas of interest based on the obtained optical spectra data and a learned model.

[0293] The learned model may relate uniformity data to the optical spectral data.

[0294] The learned model may be generated using machine learning, for example. The machine learning may include a supervised learning model selected from the group consisting of linear models, support vector machine models, decision tree models, random forest models and Gaussian models for example.

[0295] The learned model may be generated by correlating optical spectral data from a plurality of measurement locations on the wafer to uniformity data for the wafer, for example wherein the uniformity data includes at least one of thickness data, critical dimension data, depth data and material density data, which for example may be accurately measured using one or more known metrology methods.

[0296] The metrology apparatus (for example the processor 31) may further comprise a spatial modelling module that generates a spatial distribution model of the dimension of interest for the side or surface of the wafer based on the dimensions at the plurality of points or areas of interest.

[0297] In addition, the spatial modelling module may also use the mass or change in mass for the wafer measured by the mass metrology station 7 when generating the spatial distribution model, for example, the mass or change in mass may be used by the spatial modelling module as a constraint for the spatial distribution model.

[0298] Alternatively, the metrology apparatus (for example the processor 31) may comprise a modelling module that generates wafer uniformity data based on the obtained optical spectra data and a learned model, wherein the mass and / or change in mass for the wafer from the mass metrology station is optionally also used to generate the wafer uniformity data. The learned model may relate uniformity data to the optical spectral data and optionally to the mass and / or change in mass of the wafer.

[0299] In one embodiment, the following specific steps may be performed to process the hyperspectral imaging data and mass and / or change in mass data:

[0300] • Use intensity data from one or more wavelength bands from the hyperspectral imaging data to establish a coordinate system for the wafer.

[0301] • Optionally create a die map of the wafer.

[0302] • Discard hyperspectral imaging data from outside zones / areas of interest on the wafer based on the coordinate system established above.

[0303] • Process the optical information from the zones / areas of interest across the wafer to determine the within-wafer uniformity.

[0304] One or more of the above steps may involve the use of mass and / or change in mass data for the wafer obtained from one or more of a mass metrology measurement for the wafer before processing of the wafer and a mass metrology measurement for the wafer after processing of the wafer.

[0305] • A machine learning model may be created combining the mass and / or change in mass data and / or the hyperspectral imaging data. The machine learning model may be used to predict the within-wafer uniformity of text wafers.

[0306] • One or more of the above steps may involve using centre of mass information (measured separately) for the wafer when determining the within wafer uniformity.

[0307] Suitable data processing methods are described in US10,989,652B2 for example, the whole contents of which are incorporated herein by reference.

[0308] Hyperspectral imaging may be performed for the same wafer both before and after processing of the wafer, and the hyperspectral imaging data from both before and after the processing of the wafer may be used to determine the uniformity information.

[0309] Other types of assessment of the wafer may be performed in addition to, or instead of, uniformity data. For example, the hyperspectral imaging data may be used to determine bowing or curvature of the wafer using achromatic defocus imaging.

[0310] For example, as illustrated in Figure 9, the hyperspectral imaging data may include, or be used to generate, a plurality of images of the side or surface of the wafer for different wavelengths or ranges or bands of wavelengths of illumination. For example, Figure 9 illustrates a first image 57 of the wafer obtained at a first wavelength or range or band of wavelengths and a second image 59 of the wafer obtained at a second wavelength or range or band of wavelengths of the wafer.

[0311] When the wafer is bowed, i.e. the wafer is not flat, each of the plurality of images will include areas that are in focus and areas that are out of focus. For example, in focus areas 61 and out of focus areas 63 are illustrated in the two images in Figure 9.

[0312] Using one or more image processing algorithms, the pattern of focus and defocus areas in each of the plurality of images may be analysed and a shape of the wafer (for example an amount and shape of curvature or bow of the wafer) may be determined based on the analysis.

[0313] Information on the shape of the wafer may be combined with other data determined based on the hyperspectral imaging data and / or mass metrology data (mass and / or change in mass) to determine other information about the wafer. For example, the shape of the wafer determined as described above may be combined with information on the thickness of the wafer and / or a film on the side or surface of the wafer determined based on the mass metrology data and / or the hyperspectral imaging data to determine a stress in the film. For example, the stress in the film may be calculate on a global or local level based on curvature information of the wafer.

[0314] Of course, it is not necessary to use all of the hyperspectral imaging data for performing this analysis. For example, this analysis can be performed using one or more channels of the imaging data. Figure 10 is a schematic illustration of a metrology apparatus according to an embodiment of the present invention. The metrology apparatus is a modified version of the metrology apparatus 41 illustrated in Figure 6 and described above (or alternatively is a modified version of the metrology apparatus 49 illustrated in Figure 7 and described above).

[0315] In particular, the metrology apparatus of Figure 10 is modified to include an interferometer reference unit 65, to enable interference measurement for the wafer. The interferometer reference unit 65 comprises a reference wafer 67 that is supported on a support 69. The interferometer reference unit 65 further comprises a lens (or other optics) for directing light that has passed through the beam splitter 43 onto the reference wafer 67.

[0316] Light that is reflected from the reference wafer 67 and is then incident on the hyperspectral imaging camera 26 will interfere with light that is reflected from the wafer 25 and is then incident on the hyperspectral imaging camera 26.

[0317] By analysing an interference pattern produced by this interference and imaged by the hyperspectral imaging camera 26, it may be possible to identify differences between the wafer 25 and the reference wafer 67, for example differences in bow or curvature of the wafer, differences in edge profile of the wafer, or differences between macro features on the side or surface of the wafer and macro features on the side or surface of the reference wafer.

[0318] Of course, when performing such an analysis it is not necessary to use all of the hyperspectral imaging data obtained by the hyperspectral imaging camera 26. Instead, one or a sub-set of channels (i.e. distinct frequencies or bands of frequencies) can be used for the analysis.

[0319] Figure 11 illustrates an example of measurement data obtained using the metrology apparatus of Figure 10.

[0320] Figure 11 shows an edge profile 71 of the wafer 25, and an interference pattern 73 produced by interfering light from the edge of the wafer 25 and from the edge of the reference wafer 67. The interference pattern 73 can be analysed to determine the similarity or otherwise between the edge of the wafer 25 and the edge of the reference wafer 67, and / or to determine or measure the wafer edge profile of the wafer 25.

[0321] The edge profile information may be combined with the mass and / or change in mass measurement for the wafer to determine mass loss during an edge cleaning process performed on the wafer.

[0322] Figure 12 is a schematic illustration of part of a metrology apparatus according to an embodiment of the present invention. In particular, Figure 12 illustrates a hyperspectral imaging system 75 that may be used as part of a metrology apparatus according to the invention. For example, the hyperspectral imaging system 75 may be used in place of the hyperspectral imaging system 23 of the embodiments of Figure 2, Figure 3, Figure 4, and / or Figure 5. The embodiment of Figure 12 may therefore include any of the features of the embodiments of Figures 2-5, unless incompatible, and vice versa. The hyperspectral imaging system 75 includes a support 76 for supporting the wafer during hyperspectral imaging of the wafer 25. The support 76 may either be configured as a simple support, e.g. comprising a chuck or a plate, or as a temperature changing part, depending on the specific embodiment. For example, where the hyperspectral imaging system 75 is used as part of the metrology apparatus 21 of Figure 2, the support 76 may correspond to the first temperature changing part 17. Where the hyperspectral system 75 is used as part of the metrology apparatus 33 of Figure 2, the support 76 may correspond to the second temperature changing part 19. Where the hyperspectral system 75 is used as part of the metrology apparatus 35 of Figure 4, the support 76 may correspond to the pan 15 of the device 11 . Where the hyperspectral system 75 is used as part of the metrology apparatus 37 of Figure 5, the support 76 may correspond to the support (e.g. chuck) of the hyperspectral imaging station 39.

[0323] The hyperspectral imaging system 75 further includes an illumination source implemented as a plurality of light sources 77 which are mounted around next to (e.g. adjacent to) the support 76. Two light sources 77 are depicted in Figure 12, although in practice there may be a different (e.g. greater) number of light sources mounted around the support 76. For example, the light sources 77 may be arranged in a ring around the support 76. The light sources 77 may be arranged such that they are evenly spaced around the support 76.

[0324] The light sources 77 may include any suitable type of light source. For example, the light sources 77 may be broadband light sources, such as broadband LEDs.

[0325] The hyperspectral imaging system 75 further includes a reflector in the form of a concave reflective surface 78. The concave reflective surface 78 faces towards the support 76 and the light sources 77 arranged around the support 76, and is arranged to reflect light emitted by the light sources 77 onto the wafer 25 on the support 76. The concave reflective surface 78 may have any suitable curved or domed shape for reflecting the light towards the support 76. A central axis 79 (i.e. principal axis) of the concave reflective surface 78 may be substantially aligned with a centre (middle) of the support 76. In this manner, when the wafer 25 is on the support, the concave reflective surface 78 may be substantially centred about the wafer 25.

[0326] The concave reflective surface 78 may be configured to reflect light from the light sources 77 as diffuse light, i.e. the concave reflective surface 78 may reflect diffused light towards the wafer 25. In this manner, the wafer 25 may be illuminated with diffuse light from the concave reflective surface 78. This may result in a relatively even (smooth) illumination across the side or surface of the wafer 25.

[0327] In some cases, the concave reflective surface 78 may include a coating configured to diffuse light incident on the concave reflective surface 78. By way of example, the coating may include a white matt coating or finish may, and / or a PTFE coating on the concave reflective surface 78. As another example Spectraflect™ or Permaflect™ supplied by Labsphere may provide suitable diffuse reflecting coatings.

[0328] In some cases, a material of the concave reflective surface 78 may be selected so as to diffuse the reflective light, e.g. so that no coating may be needed. For example, the concave reflective surface 78 may be made of an acrylic material, which may have suitable light diffusing properties. The hyperspectral imaging system 75 further includes a hyperspectral imaging camera 80 that is configured to perform hyperspectral imaging of, or obtain a hyperspectral image of, or obtain hyperspectral imaging data of, a side or surface of the wafer. The hyperspectral imaging camera 80 may, for example, be as described in relation to the hyperspectral imaging camera 26.

[0329] The hyperspectral imaging camera 80 is arranged to receive light reflected by the wafer 25. The hyperspectral imaging camera 80 is arranged on an opposite side of the concave reflective surface 78 compared to the support 76 and wafer 25. Thus, an aperture (opening, through-hole) is formed in the concave reflective surface 78, so that light reflected from the wafer 25 can reach the hyperspectral imaging camera 80. In the example shown, a portion (e.g. lens) of the hyperspectral imaging camera 80 protrudes through the aperture in the concave reflective surface 78, so as to receive reflected light from the wafer 25.

[0330] The arrows 81 in Figure 12 illustrate light paths in the hyperspectral imaging system 75 during hyperspectral imaging of the wafer 25. As can be seen, light emitted from the light sources 77 is emitted towards the concave reflective surface 78. The light from the light sources 77 is reflected by the concave reflective surface 78 back towards the wafer 25. As noted above, the reflected light may be diffused by the concave reflective surface 78. The wafer 25 reflects the received light, some of which is received by the hyperspectral imaging camera 80.

[0331] As shown, the hyperspectral imaging camera 80 may be mounted such that it is centred relative to the wafer 25 and / or the central axis 79 of the concave reflective surface 78. For example, the hyperspectral imaging camera 80 may be mounted at an apex of the hyperspectral imaging camera 80. This may facilitate hyperspectral imaging of the wafer 25. Alternatively, the hyperspectral imaging camera 80 may be at a position offset from the central axis 79 of the concave reflective surface 78.

[0332] The light sources 77 may be arranged such that light emitted by the light sources is angled (inclined) towards the central axis 79 of the concave reflective surface 78. This may result in a relatively small angle of incidence of the reflected light on the wafer 25, which may facilitate hyperspectral imaging of the wafer 25.

[0333] The concave reflective surface 78 may form part of a housing 82 or chamber for enclosing the wafer 25 during spectral imaging. In particular, the concave reflective surface 78 may be provided as a curved (domed) inner surface of the housing 82 which faces towards the support 76. The light sources 77 may be mounted on a surface of the housing next to (e.g. adjacent or near) the support 76, such that they face toward the concave reflective surface 78. In the example shown, the light sources 77 are mounted on a sidewall of the housing 82 which surrounds the support 76.

[0334] The description above refers to a hyperspectral imaging system. However, other embodiments of the invention may use a spectral imaging system or a multispectral imaging system, for example, instead of a hyperspectral imaging system. References to a hyperspectral imaging system and / or hyperspectral imaging camera in the above may therefore be replaced with reference to a spectral imaging system and / or spectral imaging camera, or multispectral imaging system and / or multispectral imaging camera, unless incompatible.

[0335] The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

[0336] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

[0337] For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0338] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0339] Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0340] It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and / or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means for example + / - 10%.

Claims

Claims:1 . A metrology apparatus comprising: a mass metrology station for measuring a mass and / or a change in mass of a wafer; and a spectral imaging system for performing spectral imaging of at least part of a wafer.

2. The metrology apparatus according to claim 1 , wherein the spectral imaging system is a multispectral imaging system or a hyperspectral imaging system.

3. The metrology apparatus according to claim 1 or claim 2, wherein the metrology apparatus is configured to generate wafer uniformity data based on at least an output of the spectral imaging system.

4. The metrology apparatus according to claim 3, wherein the metrology apparatus is configured to generate wafer uniformity data based on an output of the spectral imaging system and a mass and / or change in mass measured by the mass metrology station.

5. The metrology apparatus according to claim 3 or claim 4, wherein the metrology apparatus is configured to generate the wafer uniformity data using a machine learning model and / or a learned model.

6. The metrology apparatus according to any one of the preceding claims, wherein the spectral imaging system is configured to perform spectral imaging of at least part of the wafer while the wafer is in the mass metrology station.

7. The metrology apparatus according to any one of the preceding claims, wherein: the mass metrology station comprises a device for measuring the weight or mass, and / or the change in weight or mass, of a wafer, and the spectral imaging system is configured to perform spectral imaging of at least part of the wafer while the wafer is loaded on the device.

8. The metrology apparatus according to any one of the preceding claims, wherein the metrology apparatus comprises a thermalisation station for changing the temperature of a wafer.

9. The metrology apparatus according to claim 8, wherein the spectral imaging system is configured to perform spectral imaging of at least part of the wafer while the wafer is in the thermalisation station.

10. The metrology apparatus according to claim 8 or claim 9, wherein: the thermalisation station comprises a temperature changing device for changing the temperature of the wafer, and the spectral imaging system is configured to perform spectral imaging of at least part of the wafer while the wafer is loaded on the temperature changing device.

11. The metrology apparatus according to claim 10, wherein the temperature changing device comprises: a passive temperature changing device; or an active temperature changing device.

12. The metrology apparatus according to any one of claims 8 to 11 , wherein the metrology apparatus comprises a wafer handling system for loading a wafer into the mass metrology station and for loading a wafer into the thermalisation station.

13. The metrology apparatus according to any one of claims 8 to 12, wherein the metrology apparatus comprises a first thermalisation station and a second thermalisation station, and wherein: the spectral imaging system is configured to perform spectral imaging of at least part of the wafer while the wafer is in the first thermalisation station; or the spectral imaging system is configured to perform spectral imaging of at least part of the wafer while the wafer is in the second thermalisation station.

14. The metrology apparatus according to any one of claims 1 to 5, wherein the metrology apparatus comprises a spectral imaging station comprising the spectral imaging system.

15. The metrology apparatus according to claim 14, wherein the metrology apparatus comprises a wafer handling system for loading the wafer into the mass metrology station and for loading the wafer into the spectral imaging station.

16. The metrology apparatus according to claim 14 or claim 15, wherein the spectral imaging station comprises a support for supporting a wafer during spectral imaging of at least part of the wafer.

17. The metrology apparatus according to any one of the preceding claims, wherein the spectral imaging system comprises: an illumination source; and a detector for obtaining spectral imaging data.

18. The metrology apparatus according to claim 17, wherein: the detector comprises a hyperspectral imaging camera.

19. The metrology apparatus according to claim 17 or claim 18, wherein the illumination source comprises a broadband light source.

20. The metrology apparatus according to claim 17, wherein: the illumination source is operable to select a specific wavelength or specific range of wavelengths of illumination.

21. The metrology apparatus according to claim 20, wherein the illumination source comprises: a plurality of illumination sources each having a different wavelength or range of wavelengths, wherein the plurality of illumination sources are configured to be operated independently; or an illumination source having a tuneable or selectable wavelength or range of wavelengths of illumination.

22. The metrology apparatus according to claim 17, wherein the spectral imaging system comprises a filter for selectively transmitting a specific wavelength or range of wavelengths of the illumination.

23. The metrology apparatus according to claim 22, wherein the filter comprises one or more of: a plurality of band pass filters, each of which is configured to transmit a different specific wavelength or range of wavelengths of illumination; a tuneable filter that is tuneable to selectively transmit a specific wavelength or range of wavelengths of illumination; a diffraction grating; or a light dispersion device.

24. The metrology apparatus according to any one of claims 17 to 23, wherein the spectral imaging system further comprises optics configured to direct illumination from the illumination source onto a wafer, and to direct illumination from the wafer to the detector.

25. The metrology apparatus according to any one of claims 17 to 23, wherein the spectral imaging system further comprises a reflector configured to reflect light from the illumination source onto the wafer, and wherein the detector is arranged to receive light reflected from the wafer.

26. The metrology apparatus according to claim 25, wherein the reflector comprises a concave reflective surface arranged to reflect the light from the illumination source onto the wafer.

27. The metrology apparatus according to claim 25 or 26, wherein an aperture is formed in the reflector, and the detector is arranged to receive light reflected from the wafer through the aperture in the reflector.

28. The metrology apparatus according to any one of claims 25 to 27, wherein the reflector is configured to reflect the light from the illumination source as diffuse light.

29. The metrology apparatus according to any one of the preceding claims, wherein the metrology apparatus is configured to determine a dimension of the wafer at a plurality of locations on the wafer based on the output of the spectral imaging system and a machine learning model and / or a learned model.

30. The metrology apparatus according to claim 29, wherein the metrology apparatus is further configured to generate a spatial distribution model of the dimension based on at least the determined dimension at the plurality of locations.

31. The metrology apparatus according to claim 30, wherein the metrology apparatus is configured to generate the spatial distribution model of the dimension based on the determined dimension at the plurality of locations and the mass and / or change in mass for the wafer measured by the mass metrology station.

32. The metrology apparatus according to any one of the preceding claims, wherein the metrology apparatus is configured to determine information regarding a bow or curvature of the wafer from the output of the spectral imaging system.

33. The metrology apparatus according to claim 32, wherein the metrology apparatus is configured to: obtain a plurality of images at different wavelengths or ranges of wavelengths using the spectral imaging system; analyse a defocus pattern in each of the plurality of images; and determine information regarding a bow or curvature of the wafer from the results of the analysis.

34. The metrology apparatus according to any one of the preceding claims, wherein the metrology apparatus is configured to perform optical interferometry between the wafer and a reference wafer.

35. The metrology apparatus according to claim 34, wherein the metrology apparatus comprises a reference unit comprising a reference wafer, and wherein the spectral imaging system is configured to perform interferometry between the wafer and the reference wafer.

Images