Method and apparatus for measuring the temperature of a semiconductor wafer

Abstract

The present application relates to methods and apparatus for measuring the temperature of a semiconductor wafer The method involves using a thermometry device to irradiate the semiconductor wafer with a focussed excitation light source to stimulate emission of a Raman scattered light signal from the semiconductor wafer; detecting the Raman scattered light signal emitted from the semiconductor wafer; determining a Raman-derived temperature of the semiconductor wafer from information relating to the Raman scattered light signal; and using an autofocus system to monitor the focal position of the excitation light source and adjusting the thermometry device so as move the focal position to optimise the detected Raman scattered light signal. Also disclosed is a method using both Raman and photoluminescence signal to determine the temperature of a semiconductor wafer.

Description

[0001] METHOD AND APPARATUS FOR MEASURING THE TEMPERATURE OF A SEMICONDUCTOR WAFER

[0002] FIELD OF THE INVENTION

[0003] The invention relates to methods for measuring the temperature of semiconductor wafers, as well as temperature-sensing apparatus for conducting such measurements, and waferprocessing equipment incorporating such temperature-sensing apparatus.

[0004] BACKGROUND

[0005] Controlling and monitoring the temperature of semiconductor wafers during processing can be very important to successfully, efficiently and consistently achieving desired treatments. However, temperature monitoring during processing represents a significant technical challenge, given the need to avoid sample contact and contamination, and to operate in a dynamic environment across a range of sample and treatment conditions.

[0006] At a commercial level, Cl-Semi Systems offer thermometry systems compatible with semiconductor wafer processing equipment. The company’s NTM product line encompasses a range of systems for in-situ wafer temperature monitoring based on emissivity-corrected pyrometry. These systems measure the infra-red thermal radiation emitted by the sample at a given temperature. However, such systems have limitations which impact their versatility and accuracy.

[0007] Firstly, emissivity-corrected pyrometry struggles to report accurate temperatures in situations where the wafer surface includes structures, such as the types of hard mask commonly used in wafer processing steps. Emissivity corrected pyrometry also requires calibration and room-temperature baseline measurements to be conducted after each measurement.

[0008] Secondly, emissivity-corrected pyrometry often requires sensors positioned on both sides of a wafer, or at least an emitter-receiver pair on opposite sides of the wafer, to include transmissivity information in the data evaluation. This is unfeasible in systems where one side of the wafer is occupied by a heating system, such as an optical heating system, as this would distort the measurements conducted on this side of the wafer.

[0009] Another thermometry technique suggested for use in semiconductor wafer processing is band edge thermometry. Here, a luminescence spectrum is obtained for a sample, from which the bandgap energy can be derived from the centre of mass of the distribution of the spectrum. The temperature of the sample can then be deduced from this information.

[0010] The type of detector used in band edge thermometry depends on the wavelengths of the spectral data collected from the samples. For certain semiconductor material samples such as silicon, GaAs, and InP, which have room-temperature bandgap energies in the range 1 - 1.5 eV, expensive InGaAs detectors are typically used.

[0011] Furthermore, band edge thermometry relies on spectrally complete photoluminescence data because it uses the width of the spectrum around the band edge to calculate the temperature of a sample. This can be problematic for measuring the temperature of samples heated by the type of optical heaters commonly used in semiconductor wafer processing, as spurious signals arising from the optical heater can interfere with the photoluminescence signals from the sample.

[0012] Measuring the temperature of a sample using Raman spectroscopy has also been suggested. For example, JPH07218355A describes a temperature measuring method, temperature measuring apparatus, and semiconductor manufacturing apparatus which uses Raman scattered light for measuring the temperature of a semiconductor wafer surface in a non-contact manner. However, existing proposals based on Raman-based thermometry have not been adopted into common use, presumably due to challenges arising from the relatively poor signal-to-noise ratio (SNR) of the Raman signal, particularly in the noisy environment created by the use of optical heaters.

[0013] Hence, there remains a need for improved techniques for measuring the temperature of semiconductor wafers during processing, in particular techniques which provide improved accuracy and flexibility.

[0014] SUMMARY OF THE INVENTION

[0015] To address the unmet need mentioned above, the present inventors have developed improved methods of Raman-based thermometry compatible with semiconductor processing apparatus and conditions, overcoming challenges to do with the low SNR typically displayed by such measurements. The inventors have recognised that Raman-based thermometry provides an excellent basis on which to carry out thermometry of semiconductor wafers undergoing processing, because the relationship between temperature and signal is relatively insensitive to wafer and processing conditions (such as level of doping, the presence of surface layers such as masks, and the presence of dispense liquids).

[0016] To this end, in a first aspect the present invention combines Raman-based thermometry with photoluminescence-based thermometry, in order to achieve accurate wafer-independent temperature measurement. More specifically, the invention provides a method of measuring the temperature of a semiconductor wafer, using a thermometry device comprising an excitation light source and a detection system, the method comprising steps of: irradiating the semiconductor wafer with the excitation light source to stimulate emission of a Raman scattered light signal from the semiconductor wafer and a photoluminescence emission signal from the semiconductor wafer; simultaneously detecting the Raman scattered light signal and photoluminescence signal emitted from the semiconductor wafer using the detection system; determining a Raman-derived temperature of the semiconductor wafer from information relating to the Raman scattered light signal; deriving a calibrated equation relating temperature to the photoluminescence emission signal based on the Raman-derived temperature; and carrying out a further measurement of the photoluminescence signal and determining the temperature of the semiconductor based on the calibrated equation.

[0017] Advantageously, this methodology allows an accurate measurement of temperature to be obtained in a wafer-independent manner. Specifically, the inventors have recognised that whilst the SNR of Raman-based measurement is generally low, the relationship between Raman signal and temperature is relatively independent of the specifics of a wafer (such as the presence of doping, coatings and liquid dispense). For example, the relationship between Raman signal and temperature for a silicon wafer with a hard mask corresponds to that of the underlying silicon wafer. Thus, the inventors have recognised that by taking multiple Raman-based measurements and using this to carry out an on-the-fly calibration of the (wafer-dependent) relationship between photoluminescence and temperature, the impact of inaccuracy in the Raman-measurements can be reduced (due to obtaining multiple datapoints) and the measurement methodology shifted to higher SNR photoluminescence. In particular, once calibrated the method allows an instantaneous measure of temperature using photoluminescence, which is more accurate than if that instantaneous measure were derived from Raman spectroscopy alone.

[0018] In a second aspect, the present inventors have also developed a method to improve the accuracy and flexibility of Raman-based thermometry by carrying out on-the-fly optimisation of the signal using an autofocus system. More specifically, in a second aspect the invention provides a method of measuring the temperature of a semiconductor wafer, using a thermometry device comprising an excitation light source, a detection system, and an autofocus system, the method comprising the steps of: irradiating the semiconductor wafer with a focussed excitation light source to stimulate emission of a Raman scattered light signal from the semiconductor wafer; detecting the Raman scattered light signal emitted from the semiconductor wafer using the detection system; determining a Raman-derived temperature of the semiconductor wafer from information relating to the Raman scattered light signal; and using the autofocus system to monitor the focal position of the excitation light source and adjust the thermometry device so as move the focal position to optimise the detected Raman scattered light signal.

[0019] In separate aspects, the present invention also provides wafer processing apparatus for carrying out the methods of the first and second aspects of the invention.

[0020] For example, a third aspect of the invention provides an apparatus for treating a semiconductor wafer, the apparatus comprising: a treatment chamber; a wafer support for holding a semiconductor wafer; and a thermometry device for measuring the temperature of a semiconductor wafer positioned on the wafer support, the thermometry device comprising: an excitation light source for irradiating a semiconductor wafer held on the wafer support with a excitation light to stimulate emission of Raman scattered light signal from the semiconductor wafer; a detection system configured to detect a Raman scattered light signal and photoluminescence signal emitted from a semiconductor wafer held on the wafer support; and a processor configured to determine a Raman-derived temperature of the semiconductor wafer from information relating to the Raman scattered light signal, and derive a calibrated equation relating temperature to the photoluminescence emission signal based on the Raman-derived temperature, and measure the temperature of the semiconductor wafer from the calibrated equation.

[0021] A fourth aspect of the invention provides wafer processing apparatus for treating a semiconductor wafer, the apparatus comprising: a treatment chamber; a wafer support for holding a semiconductor wafer; and a thermometry device for measuring the temperature of a semiconductor wafer positioned on the wafer support, the thermometry device comprising: an excitation light source for irradiating a semiconductor wafer held on the wafer support with a focussed excitation light to stimulate emission of Raman scattered light signal from the semiconductor wafer; a detection system configured to detect a Raman scattered light signal emitted from a semiconductor wafer held on the wafer support; and an autofocus system to monitor the focal position of the excitation light source and adjust the focal position to optimise the detected Raman scattered light signal.

[0022] A fifth aspect of the invention provides a thermometry device suitable for use in the methods of the first and second aspects, and the apparatus of the third and fourth aspects. In particular, the invention provides thermometry devices which can be retrofitted to conventional wafer processing apparatus.

[0023] In an exemplary embodiment of this fifth aspect, the present invention provides a thermometry device comprising: an excitation light source; optionally, an excitation light filter; an excitation optical fibre for receiving light from the excitation light source; a collimating lens, for collimating the excitation light exiting the excitation optical fibre; an objective lens, to focus the excitation light into a focal plane positioned at a semiconductor wafer in use; a detection optical fibre to collect emitted signal from a semiconductor wafer in use, the detection optical fibre having an end face; an emission lens for focussing the emitted signal onto the end face of the detection optical fibre; a beamsplitter, to separate excitation light from emitted signal;

[0024] - wherein the excitation optical fibre, collimating lens, objective lens, detection optical fibre, emission lens and beamsplitter are mounted on or within a probe head; an actuator attached to the probe head, for moving the probe head relative to a semiconductor wafer in use; a detection system comprising: a detector; a dispersive element for spectrally separating wavelengths ahead of the detector; optionally, an emission filter; and an autofocus system, comprising: a reflection optical fibre, for receiving reflected excitation light from a semiconductor wafer in use; a sensor for measuring the intensity of the reflected excitation light from the reflection optical fibre; a processor to actuate the actuator attached to the probe head in response to the intensity of the reflected excitation light from the reflection optical fibre.

[0025] The methods, devices and apparatus of the present invention are suitable for measuring the temperature of silicon-based semiconductor wafers, but also semiconductor wafers made from other materials, including but not limited to germanium-based materials, carbon-based materials, selenium-based materials, arsenic-based materials, tellurium-based materials, boron-based materials, gallium-based materials, aluminium-based materials, and indium- based materials.

[0026] These semiconductor materials may be predominantly of one element, for example a Group IV element such as silicon or germanium. Alternatively, the semiconductor material may be a chemical compound, such as a carbide, a pnictide (e.g. nitride or arsenide) or a chalcogenide (e.g. oxide or sulfide), for example a chemical compound which is a carbide, nitride or chalcogenide of a Group III or (preferably) Group IV element. Examples of such materials may include, for example, silicon nitride, silicon carbide, gallium nitride, gallium arsenide, indium phosphide, indium gallium arsenide, or sapphire, and each of the polytypes of these materials.

[0027] The semiconductor material may be a single crystalline material or a polycrystalline material. In one embodiment the semiconductor material is a single crystalline silicon material.

[0028] The semiconductor material may also include a dopant, such as a p-type dopant or n-type dopant. For example, in instances where the semiconductor material is or incorporates a Group IV element, the dopant may be a n-type dopant such as boron, aluminium, gallium or indium; or p-type dopant such as phosphorus, arsenic, antimony, bismuth or lithium.

[0029] Preferably, the semiconductor material is a silicon-based material. For example, the semiconductor material may be silicon, silicon carbide (SiC), silicon nitride (SiN) or silicon oxide, optionally doped with an n-type dopant or p-type dopant as recited above. Optionally, the semiconductor material includes a surface layer of an alternative material, e.g. applied by coating or deposition. Preferably, the surface layer is an additional semiconductor material. For example, the semiconductor material may be a silicon wafer bearing a surface layer of an alternative material such as silicon oxide or silicon nitride.

[0030] The surface layer may be, for example, no more than 1000 nm, no more than 500 nm, no more than 300 nm or no more than 200 nm, no more than 100 nm, no more than 50 nm, or no more than 10 nm. For example, the surface layer may be no more than 200 nm.

[0031] Preferably, the semiconductor material does not include a surface metal layer.

[0032] If photoluminescence alone was used to determine the temperature of this variety of materials, the material would need to be well-characterised prior to measurement and a suitably pre-calibrated equation used to determine the temperature based on photoluminescence. Advantageously, the methods of the present invention require less characterisation of the sample prior to measurement, since the relationship between Raman signal and temperature is less dependent on the specifics of the sample.

[0033] Advantageously, the methods of the present invention may also be used to distinguish between the polytypes of a given material from which the semiconductor wafer is made at each measured temperature. The methods of the present invention can therefore be used to determine changes in polytype morphology as a function of temperature. Preferred and optional features of the invention are set out in the claims, and discussed in more detail below.

[0034] BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Embodiments of the invention are discussed below with reference to the accompanying drawings, in which:

[0036] Figure 1 is a schematic side view of wafer processing apparatus, with the temperature of a semiconductor wafer being measured by a thermometry device of the invention;

[0037] Figure 2 is a top view of the fluid dispensing system of Figure 1 moving into position to deliver fluids to the semiconductor wafer;

[0038] Figure 3 is a schematic representation of the thermometry device used in Figure 1 ;

[0039] Figure 4 is an internal view of components of the sensor head of the thermometry device of Figure 3;

[0040] Figure 5 is an internal view of components of the detector of the thermometry device of Figure 3; Figure 6 is a plot showing Raman signal obtained on a silicon wafer, displaying anti-Stokes (AAS) and Stokes (As) peaks;

[0041] Figure 7 is a plot showing variation of the anti-Stokes peak from the silicon wafer of Figure 6 with temperature;

[0042] Figure 8 is a plot showing variation of the Stokes peak from the silicon wafer of Figure 6 with temperature;

[0043] Figure 9 is a plot showing that the ratio of the area of anti-Stokes and Stokes peaks is proportional to temperature for the same spot on a silicon wafer;

[0044] Figure 10 is a plot showing the ratio of the area of anti-Stokes and Stokes peaks at 10 different positions on a silicon wafer, showing consistency of the results achieved;

[0045] Figure 11 is a plot showing the ratio of the area of anti-Stokes and Stokes peaks for a range of different semiconductor wafer types;

[0046] Figure 12 is a plot showing a calibration of equation (i) using a reference wafer mounted with an infrared thermal sensor;

[0047] Figure 13 is a plot showing time-course temperature measurements of a semiconductor wafer in absence of autofocus or manual focus corrections in comparison to known reference temperatures; and

[0048] Figure 14 is a plot showing temperature measurements of a semiconductor wafer as a function of the position of the semiconductor wafer in relation to its focal point.

[0049] DETAILED DESCRIPTION OF THE INVENTION

[0050] 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.

[0051] Raman-derived temperature determination

[0052] The methods of the invention involve determining a Raman-derived temperature from the Raman scattered light signal from a semiconductor wafer.

[0053] Preferably, the Raman-derived temperature is derived from a ratio between the anti-Stokes signal and the Stokes signal of the Raman scattered light signal. The ratio between the anti- Stokes signal and the Stokes signal is largely independent of the conditions of the semiconductor wafer and so is, in this regard, a robust indicator for temperature. That is, the Raman-derived temperature, Tu, may be related to the Stokes signal, St, and Tithe anti-Stokes signal, Aitsuch that Tual / s.

[0054] The Raman-derived temperature, T1;i, is hence preferably measured in accordance with the calibrated equation (i):

[0055] (D Tu= a^ + b

[0056] Where a and b are Raman-derived temperature calibration coefficients.

[0057] Typically, the anti-Stokes signal and Stokes signal used in the calculation correspond to Area under the Curve (AUC) values.

[0058] The anti-Stokes and Stokes signal may correspond to values for one or more representative individual peaks in the Raman spectrum. Optionally, the area under the curve is calculated by fitting each anti-Stokes or Stokes peak. Alternatively, the area under the curve is determined by summing / binning all relevant signal corresponding to each peak. This latter option is computationally simpler and faster.

[0059] Optionally, since the relationship between Raman signal and temperature is relatively robust to changes in the semiconductor wafer, the Raman temperature may be calculated based on a pre-determined equation, i.e. with pre-set values for a and b. For example, when the semiconductor wafer comprises a surface layer of an additional material or a fluid dispense, the values of a and b will generally correspond to those for the underlying semiconductor wafer material, e.g. if the semiconductor wafer is a silicon wafer with a surface layer of SiN or SiO, the values for a and b will generally correspond to those derived for a pure silicon wafer.

[0060] Coefficients a and b can be theoretical values, from ab initio calculation based on theory. Therefore, optionally, a and b correspond to theoretical values.

[0061] It is known to the skilled person that the intensity ratio of Stokes to anti-Stokes signals can be related to phonon frequency, a>, by an equation as follows:

[0062] Where h is the reduced Planck’s constant and fe is the Boltzmann constant.

[0063] See Hart et al, Temperature dependence of Raman scattering in silicon, Phys Rev B, 1 (2), 1970, page 641 section III.C. For any 7) > 0, this equation can be expressed as a Taylor series expansion at point To, subsequently truncated after the first order, and rearranged to give the expression:

[0064] From which coefficients a and b can be derived as:

[0065] However, typically the best-fit coefficients deviate from the values calculated by theory due to different levels of dispersion at the Stokes and anti-Stokes wavelengths. Therefore, preferably coefficients a and b are determined by measurement.

[0066] Calibration of equation (i) may be carried out in a separate control experiment.

[0067] Various methods for calibrating equation (i) are possible.

[0068] In a first method, a reference wafer may be added to a temperature-controlled environment (such as a hot-plate or a temperature-controlled chamber) and allowed to equilibrate so as to achieve a known target temperature, and the Raman spectrum determined.

[0069] In a second method, the reference wafer may be measured using a separate (e.g. contact) based thermometry method to determine the temperature and the Raman spectrum determined. For example, the wafer may be mounted with a thermal sensor to provide a separate reading of the surface temperature. In one embodiment, the equation may be calibrated using a reference wafer mounted with a thermal sensor, wherein the reference wafer is made from the same semiconductor material as the target semiconductor wafer. The reference wafer is irradiated by an excitation light source to produce a Raman scattered light signal, which is calibrated with respect to the known temperature of the reference wafer derived using the mounted thermal sensor. As the reference wafer is made from the same semiconductor material as the target semiconductor wafer, the Raman signal emitted by the semiconductor wafer during measurement corresponds with the Raman signal emitted by the reference wafer. Suitable reference wafers are available commercially, for example the SensArray® (SA) Wafer available from KLA Corporation, California.

[0070] In a third method, the equation (i) is calibrated using a silicon reference wafer doped with a material which allows temperature to be determined using conventional infrared emissivity thermometry (e.g. a thermal imaging camera), where the dopant does not alter (at least to any significant extent) the relative signal intensity of the Stokes and Anti-Stokes peaks. The reference wafer may be doped with n- or p-type dopant material, such as the dopants mentioned above. For example, the reference wafer may be doped with phosphorus or boron. Advantageously, the reference wafer may be doped to an extent where the transmissivity of the wafer is reduced to a point where conventional infrared emissivity thermometry can be used. In one embodiment, the doped reference wafer has a transmissivity of no more than 20%, no more than 15%, no more than 10%, no more than 5%, no more than 1 %, and no more than 0.1%. In one embodiment the reference wafer may be doped with n- or p-type dopant to a concentration of at least 0.1 x1018dopant atoms per cm3(dop / cm3) of wafer, or at least 0.5 x1018dop / cm3, 1 .0 x1018dop / cm3, 2.0 x1018dop / cm3, 3.0 x1018dop / cm3, or 4.0 x1018dop / cm3. For example, the reference wafer may be doped to a concentration of between 1 .0 x1018dop / cm3and 5.0 x1018dop / cm3.

[0071] Calibration step

[0072] In the first aspect of the invention, the next step of the method comprises deriving a calibrated equation relating temperature to the photoluminescence emission signal. This is generally referred to herein as a “calibration step”. Since this calibration step is carried out on the target semiconductor wafer (instead of based on some reference data or sample), this calibration step may be referred to as an “on-the-fly” calibration.

[0073] Suitably, the calibration step comprises relating temperature to the photoluminescence emission signal by taking I Raman-derived temperatures, Tl hand inputting them into the equation:

[0074] T±,i =afCLi) +P where / ( is a function relating to the intensity of the photoluminescence emission signal measured at temperature 7i , and wherein resolving the equation determines calibration coefficients a and / ?.

[0075] The inventors have identified that calibrating the equation relating temperature to a logarithmic function of the photoluminescence emission signal means that the equation can be linearly calibrated over a wider range of temperatures. Hence it is preferable that the equation relating temperature to the photoluminescence emission signal is calibrated by taking / Raman-derived temperatures, Tl band inputting them into the equation:

[0076] Tw= a log(Li) + p

[0077] Advantageously, relating the temperature to a logarithmic function of the photoluminescence emission signal means that a linear calibration can be performed over a wider range of temperatures. This is advantageous as it allows the temperature of a semiconductor wafer to be accurately measured across a wide thermal range, such as between 20 °C and 500 °C.

[0078] The inventors have also identified that it is preferable that the equation relating temperature to the photoluminescence emission signal inputs a normalised photoluminescence emission signal. In particular, it is preferable that the photoluminescence signal is normalised based on at least one of (i) a Stokes signal obtained from the information relating to the Raman scattered light signal, (ii) an elastically scattered light signal emitted from the sample, and (iii) a reflected light signal reflected from the sample. Hence it is preferable that the equation relating temperature to the photoluminescence emission signal is calibrated by taking / Raman-derived temperatures, Tland inputting them into equation (1):

[0079] (1) T14= alog g) + ? where / is an integer greater than or equal to 2, Ltis the intensity of the photoluminescence emission signal, Xtis the intensity of at least one of a Stokes signal obtained from the information relating to the Raman scattered light signal, an elastically scattered light signal emitted from the sample, and a reflected light signal reflected from the sample, and wherein resolving equation (1) determines calibration coefficients a and / ?.

[0080] Normalising the photoluminescence emission signal to the elastically scattered light signal (also known as a Rayleigh scattered light signal) and / or to the reflected light signal (also known as a Fresnel reflected light signal) improves the SNR of the photoluminescence emission signal due to the strong signal intensities of the elastically scattered light signal and the reflected light signal.

[0081] Normalising the photoluminescence emission signal to the Stokes signal improves the resilience of the measured temperature to sample specific properties and conditions, such as doping type and amount, coatings, and fluid dispense on the semiconductor wafer.

[0082] Preferably, the method involves an initial step of heating the semiconductor wafer, and calibration of the equation relating temperature to the photoluminescence emission signal is carried out during an initial heating of the semiconductor wafer. Advantageously, calibrating the equation during this initial heating allows multiple datapoints to be used in calibrating the relationship, helping to improve the accuracy of the calibration. In terms of improving the accuracy of the temperature measurement, it is desirable that the number of measurements, N, of the Raman scattered light signal and the photoluminescence emission signal is higher in order to suppress noise in the resulting calibration coefficients a and f> inherited from the Raman scattered light signal. The SNR of the calibration coefficients scales approximately is the SNR°fthecalibration coefficients a and / ?.

[0083] The calibration step may be based on / V measurements where / V is at least 2, at least 3, at least 4, at least 5 or at least 10 measurements.

[0084] Calibration of the equation may be achieved by applying a numerical fitting function to the / V datapoints. For example, the values for a and / ? may be obtained from applying a numerical fitting function to a plot of Ti;iagainst log(Li) or log (X / L). The numerical fitting may be, for example, a Least-Squares fitting.

[0085] The calibration step allows coefficients a and / ? to be acquired on-the-fly. As a result, the temperature of a semiconductor wafer can be subsequently calculated continuously and without the need to perform baseline measurements at a particular temperature between samples or after each measurement.

[0086] Optionally, the semiconductor wafer may be provided in a treatment chamber equipped with a temperature reference device (such as a resistance thermometer, for example a PT100 platinum resistance thermometer), to measure the thermal stability of the wafer measurement environment.

[0087] In addition, in these embodiments of the present invention the calibration coefficients can be updated on demand or continuously, and so equation (1) can be automatically recalibrated, e.g. during wafer processing.

[0088] For example, the calibration step may be repeated after a set period of time, after a set change in measured temperature is reached (for example, a measured temperature increase of 5°C, 10°C or 20°C), or after a particular processing step has been carried out (for example, application of a dispense liquid).

[0089] It is desirable that the calibration step is repeated following any event which might substantially affect wavelength dependent dispersion. Optical dispersive properties may change due to, for example, changes in the wafer - e.g. due to the introduction or modification of a surface coating layer. Optical dispersive properties may also change, for example, due to alterations in the thermometry device, e.g. adjustment of components such as lenses and detectors, and / or components of the autofocus system when such a system is incorporated in the device. Photoluminescence-derived temperature determination

[0090] Once the calibration coefficients a and p are determined, the temperature of the sample is obtained from the equation:

[0091] T2= af(Li) +p

[0092] As noted above, it is preferable that the relationship between temperature and photoluminescence is presented as a logarithmic function, with the photoluminescence signal normalised. To this end, the formula used to relate photoluminescence to temperature is preferably according to the following equation:

[0093] T2= a log ( + p where T2is the temperature of the sample, X is the intensity of at least one of a Stokes signal obtained from the information relating to the Raman scattered light signal, an elastically scattered light signal emitted from the sample, and a reflected light signal reflected from the sample, L is the intensity of the photoluminescence emission signal, and a and p are the calibration coefficients.

[0094] The measured temperature of the sample, T2, inherits noise originating from the Raman scattered light signal through the noise of the calibration coefficients. Therefore, performing a higher number of measurements, N, of the Raman scattered light signal and the photoluminescence emission signal is desirable to suppress noise in the eventual sample temperature measurement. The number of measurements, N, required until the calibration is converged approximately follows:

[0095] Where SNR is the signal-to-noise ratio of the calibration coefficients and SNR2is the signal- to-noise ratio of the temperature of the sample.

[0096] The temperature of the sample may be determined in a temperature range up to, for example, 600°C, 500°C, 400°C, 300°C or 200°C. The lower limit of the temperature range may be, for example, at least -100°C, -50°C, or 0°C. The temperature range may be, for example, -100 °C to 500 °C, -50 °C to 400 °C, 0 °C to 300 °C, 10 °C to 200 °C, or 25 °C to 100 °C. In an exemplary embodiment, the temperature of the sample may be determined in a temperature range of 25 °C to 105 °C, or in a temperature range of 25 °C to 50 °C, or in a temperature range of 60 °C to 105 °C. Semiconductor wafer characterisation

[0097] Optionally, structural information about the sample can be obtained from Raman shift data obtained from the Raman scattered light signal.

[0098] One exemplary application of this is for characterising the polytype composition of the semiconductor wafer. As this can be measured simultaneously with temperature, the methods of the present invention can be used to evaluate the change in the polytype(s) of a sample as a function of temperature.

[0099] Using Raman spectroscopy to understand the polytype composition of a material, including semiconductor materials such as SiC, is known in the art and is within the capability of the skilled person in this technical field.

[0100] Autofocus system

[0101] In the second aspect, and in preferred implementations of the first aspect, the apparatus of the present invention comprises an autofocus system.

[0102] The present inventors have recognised that a shortcoming of prior art methods for measuring temperature using Raman spectroscopy is that the methods are unable to react to changes to the sample during processing, and that this inability to react to changes leads to poor collection of the Raman signal.

[0103] The inventors identified that poor collection of the Raman signal typically occurs due to perturbation of the focussing of the Raman excitation beam due to changes during processing. There are several factors which can contribute to the focus of a Raman scattered light signal or a photoluminescence emission signal being altered. In particular, the inventors identified several reasons why the optical path length of excitation light from the excitation light source to a semiconductor wafer might alter between measurements or between samples. A change in optical path length of the excitation light can alter the focus of the emitted Raman scattered light signal and / or photoluminescence emission signal.

[0104] Firstly, the optical path length can alter because of a change in the distance between the excitation light source and the semiconductor wafer. This could happen because of, for example, semiconductor wafer bow, wafer-to-wafer clamping height deviations, wafer structuring, or other system related influences. Some of these attributes are particularly pronounced when the wafer is being rotated during temperature measurement.

[0105] Secondly, the optical path length can alter because of a change in a medium between the excitation light source and the semiconductor wafer. Changes in medium can occur between measurements and samples because of, for example, addition of a layer of material to the wafer surface, such as a fluid dispense, hard mask, or other coating on or doping of the semiconductor wafer. Specifically, the optical path length will alter if there is a change in the refractive index of the medium or media through which the excitation light passes between the excitation light source and the semiconductor wafer.

[0106] Given the already low SNR of the Raman measurement, these additional factors further suppress the accuracy of the temperature measurement in prior art methodologies.

[0107] To address this issue, the inventors have discovered there is substantial benefit to using a thermometry device incorporating an autofocus system. Such an autofocus system incorporates a (closed) feedback loop which monitors the focal position of the excitation light source, and adjusts the focal position to optimise the detected signal. Thus, in the second aspect, and in preferred implementations of the first aspect, the step of irradiating the semiconductor wafer with the excitation light source comprises focussing the excitation light source onto the semiconductor wafer using focussing optics (an objective lens or a focussing mirror, preferably an objective lens), monitoring the focal position of the excitation light source, and adjusting the focal position to optimise the detected signal.

[0108] The step of monitoring the focal position may involve one or more of:

[0109] (i) monitoring the intensity of the Raman signal;

[0110] (ii) monitoring the intensity of the photoluminescence signal; and / or

[0111] (iii) monitoring the intensity of excitation light reflected from the semiconductor wafer.

[0112] In such implementations, the focal position is monitored by checking for a change (e.g. drop) in the detected intensity of (i)-(iii).

[0113] Advantageously, using either (i) or (ii) allows the same detection system (and hence detector) to be used to monitor focal position.

[0114] However, preferably, the step of monitoring the focal position involves monitoring the intensity of excitation light reflected from the semiconductor wafer. In such implementations, the apparatus comprises an autofocus system with a sensor configured to detect excitation light reflected from the semiconductor wafer. Advantageously, the reflected excitation light has a higher SNR than either the Raman signal or the photoluminescence signal, making the determination of the focal position more accurate. The sensor of the autofocus system is separate from the detector used to detect the Raman and photoluminescence signals, e.g. because the detection system incorporate filters to attenuate wavelengths corresponding to the excitation wavelength so as to minimise unwanted noise in the Raman and photoluminescence signals.

[0115] The autofocus system adjusts the focal position of the excitation light to optimise the detected signal. This may be achieved by altering the relative distance between the focussing optics and the semiconductor wafer. This may be done either by adjusting the position of the focussing optics (e.g. by mounting the focussing optics on a movable stage) or by adjusting the position of the semiconductor wafer.

[0116] For example, preferably excitation light is focussed via an objective lens, which also serves to collect light returning (via reflection or emission) from the semiconductor wafer, and the autofocus adjusts the position of the objective lens relative to the semiconductor wafer.

[0117] Optionally, the focal position is adjusted by moving the semiconductor wafer. This may be achieved by mounting the semiconductor wafer on a movable stage, such as a chuck. Preferably, however, the focal position is adjusted by moving the focussing optics. In particular, such an approach facilitates retrofitting of the thermometry device to conventional semiconductor processing apparatus, since the autofocus system feedback loop operates with components of the thermometry device itself, instead of having to interface with components of the semiconductor processing apparatus, such as the wafer support.

[0118] Preferably, the focal position of is no more than ±500 pm, or no more than ±400 pm, or no more than ±300 pm, or no more than ±200 pm, or no more than ±100 pm, or no more than ±50 pm relative to the point / region whose temperature is to be determined.

[0119] The numerical aperture of the objective lens used in the autofocus system may be no more than 0.95, no more than 0.90, no more than 0.85, no more than 0.80, no more than 0.75, no more than 0.70, no more than 0.65, no more than 0.60, no more than 0.55, no more than 0.50, no more than 0.45, no more than 0.40, no more than 0.35, no more than 0.30, no more than 0.25, no more than 0.20, no more than 0.16. The inventors found that a smaller numerical aperture reduced the extent of deviation in the measured temperature due to changes in the focal position of the autofocus system.

[0120] Confocal modality

[0121] Preferably, the thermometry device operates in a confocal modality.

[0122] In this scheme the excitation light source is focussed onto the semiconductor surface in use, and the detection system include an emission lens to focus detected emission through an aperture positioned in an optically conjugate plane to reject out-of-focus light. This modality is particularly valuable in instances where the apparatus incorporates a radiation heater for heating the semiconductor wafer, since such heaters can emit in wavelengths used for the Raman signal and photoluminescence signal. The confocal modality efficiently suppresses the contribution of signal from the radiation heater in such instances. This ability to suppress noise from the radiation heater represents a significant advantage in the low SNR Raman measurements used in the present invention.

[0123] The aperture may be provided by a pinhole, iris or by the end face of a detection optical fibre. Preferably, the detection system includes a detection optical fibre, and the aperture is provided by the face of the detection optical fibre.

[0124] The aperture may have a diameter of, for example, 200 pm or less, 150 pm or less, 100 pm or less, 75 pm or less, 50 pm or less, or 25 pm. For example, the aperture may have a diameter of 25 pm to 200 pm, for example 25 pm to 150 pm.

[0125] Preferably, the thermometry device also comprises an excitation optical fibre for receiving light from the excitation light source. Advantageously, providing an excitation optical fibre for transmitting excitation light to the semiconductor wafer means that a lower optical power of the excitation light source may be used due to the efficiency by which optical fibres transmit light.

[0126] The thermometry device preferably comprises: i. an excitation light source; ii. an excitation optical fibre for receiving light from the excitation light source;

[0127] Hi. a collimating lens, for collimating the excitation light source exiting the excitation optical fibre; iv. an objective lens, to focus the excitation light into a focal plane positioned at the semiconductor wafer; v. a detection optical fibre to collect emitted signal from the semiconductor wafer, the detection optical fibre having an end face; vi. an emission lens for focussing the emitted signal onto the end face of the detection optical fibre; and vii. a beamsplitter, to separate excitation light from emitted signal (preferably wherein the beamsplitter is a dichroic multiband beamsplitter).

[0128] To achieve a confocal imaging modality, the end face of the detection optical fibre is positioned in the conjugate plane to the focal plane of the objective lens.

[0129] Preferably, the thermometry device also incorporates (viii) an excitation light filter. The excitation light filter helps to improve monochromaticity of the excitation light, in particular by supressing laser side-modes. The excitation light filter may be a bandpass filter. Preferably, the thermometry device also incorporates (ix) an emission filter. The emission filter can be used to suppress unwanted wavelengths from the signal, such as to suppress signal from the excitation light source. The emission filter may be, for example, a notch filter.

[0130] In a particularly preferred embodiment, the thermometry device comprises a probe head, and all of components (ii)-(vii) above are mounted to or within the probe head. This is particularly advantageous in implementations incorporating an autofocus system, since all of components (ii)-(vii) can be mounted and aligned on the same probe head, and the position of the focal position adjusted by moving the probe head relative to the semiconductor wafer whilst preserving alignment of the components. In this regard, using the excitation optical fibre to deliver excitation light and the detection optical fibre to deliver light to the detector means that the position of the probe head can be adjusted whilst keeping the excitation light source and detector in a fixed position. This can facilitate reliable manufacture of the thermometry device, and facilitate retrofitting of the thermometry device to wafer processing apparatus.

[0131] In implementations including filters (viii) and (ix), the filters may also be mounted to or within the probe head. Additionally or alternatively, excitation light filter (viii) may be included as part of the excitation light source and / or emission filter (ix) may be included as part of the detection system.

[0132] The components (ii)-(vii) [and where relevant, filters (viii) and (ix)] may be mounted to or within the probe head using conventional means, such as threaded connections. For example, the excitation optical fibre (ii) and detection optical fibre (v) may be mounted to the probe head via SMA (subminiature version A) connectors.

[0133] As noted above, in instances where the thermometry device incorporates an autofocus system, the autofocus system preferably has means to move the objective lens relative to the semiconductor wafer. This allows the focal plane to be brought back into alignment with the semiconductor wafer. In such implementations, the thermometry device incorporates (x) an actuator to alter the position of the objective lens. The actuator may be, for example, a motor such as a linear motor (e.g. a voice coil actuator), or a piezoelectric actuator. Preferably, the actuator is a voice coil actuator.

[0134] Optionally, the actuator is associated with only a single component of the autofocus system. For example, the actuator may be mounted to the objective lens, to alter the position of the objective lens. Advantageously, this can allow rapid and accurate adjustment of the focus, due to the low mass of the objective lens. In implementations incorporating a probe head housing components (ii)-(vii), the actuator may be attached to the probe head. In this way, the position of the objective lens relative to the semiconductor wafer can be adjusted by moving the entire probe head, whilst preserving alignment of components (ii)-(vii).

[0135] In implementations incorporating an autofocus system which monitors reflected excitation light, the thermometry device also incorporates a sensor to detect the reflected excitation light. Preferably, the thermometry device also incorporates a reflection optical fibre, that is, a fibre to collect light reflected from the semiconductor wafer. Typically, the strongest signal for the reflected light will return along the same path as the excitation optical fibre.

[0136] Preferably, reflected light is prevented from simply returning to the excitation light source instead of the sensor by incorporating an optical splitter with the reflection optical fibre. In this way, the excitation light can be directed to the semiconductor wafer efficiently, but any returning signal is split between being directed to the excitation light source and the sensor.

[0137] The skilled person will appreciate that references to the excitation optical fibre being mounted to a probe head encompasses not only embodiments where a single fibre directs light from the excitation light source to the probe head, but also where the excitation light is delivered via more than one optical fibre.

[0138] The thermometry device also incorporates a detection system for detecting the Raman signal and photoluminescence signal. Preferably, the thermometry device incorporates a single detector for detecting the Raman scattered light signal and detecting the photoluminescence emission signal. It is advantageous that the Raman and photoluminescence emission signals are detected by a single detector so that these signals can be co-evaluated without requiring sophisticated calibration of measurements between detectors.

[0139] The inventors identified that for silicon and certain other semiconductor materials, the wavelengths of the Raman scattered light signal are close to the wavelengths of the photoluminescence emission signal. This means that both the Raman scattered light signal and the photoluminescence signal can be co-evaluated by a single detector.

[0140] Suitably, the detection system includes a dispersive element positioned ahead of the detector. The dispersive element can be used to spectrally separate the Stokes and antiStokes signal from the photoluminescence signal, so that their individual signal intensities can be determined. The dispersive element may be, for example, a prism or a grating.

[0141] Preferably, the detector is an array detector, to simultaneously resolve peaks at different wavelengths. The detector may be, for example, a charge-coupled device (CCD) array detector or an active-pixel detector such as a complementary metal-oxide semiconductor (CMOS) array detector. Optionally, the detector is a line sensor, to allow imaging of the emission spectrum. Advantageously, the combination of a dispersive element and array detector further help to separate signal from noise - for example, when the detection system includes a detection optical fibre such an approach allows removal of fluorescence background signals which can be generated by the detection optical fibre. This means that the apparatus can more accurately measure temperature without the processor having to be calibrated to account for fluorescence background signals.

[0142] Optionally, the detection system includes an amplifier to amplify signal from the detector. Optionally, the amplifier can selectively amplify signals within a specific frequency range. For example, the amplifier can be configured to selectively amplify signals in a range which includes the frequency of the Stokes and anti-Stokes signal. This is advantageous for improving the signal-to-noise ratio of the detected signals.

[0143] Advantageously, a silicon semiconductor wafer emits a Raman scattered light signal having a Stokes signal with a maximum intensity at 818 nm and an anti-Stokes signal with a maximum intensity at 754 nm following irradiation with excitation light having a wavelength of 785 nm. These wavelengths of the Stokes signal and the anti-Stokes signal are relatively closely positioned to the bandgap energy of silicon (~1100 nm) and so the low wavelength component of the photoluminescence emission signal can be co-evaluated with the Stokes signal and the anti-Stokes signal using a dispersive element and single detector configured to detect a relatively narrow spectrum of wavelengths.

[0144] Preferably, the detector is a silicon-based array detector, which may suitably be configured to detect visible and shortwave infra-red light. Advantageously, these are generally less expensive than alternative array detectors such as InGaAs array detectors.

[0145] Taking into account the comments above, a particularly preferred implementation of the thermometry device comprises: an excitation light source; optionally, an excitation light filter; an excitation optical fibre for receiving light from the excitation light source; a collimating lens, for collimating the excitation light exiting the excitation optical fibre; an objective lens, to focus the excitation light into a focal plane positioned at the semiconductor wafer; a detection optical fibre to collect emitted signal from the semiconductor wafer, the detection optical fibre having an end face; an emission lens for focussing the emitted signal onto the end face of the detection optical fibre; a beamsplitter, to separate excitation light from emitted signal;

[0146] - wherein the excitation optical fibre, collimating lens, objective lens, detection optical fibre, emission lens and beamsplitter are mounted on or within a probe head; an actuator attached to the probe head; a detection system comprising: a detector; a dispersive element for spectrally separating wavelengths ahead of the detector; optionally, an emission filter; an autofocus system, comprising: a reflection optical fibre, for receiving reflected excitation light from the semiconductor wafer; a sensor for measuring the intensity of the reflected excitation light from the reflection optical fibre; and a processor to actuate the actuator attached to the probe head in response to the intensity of the reflected excitation light from the reflection optical fibre (thereby repositioning the objective lens relative to the semiconductor wafer).

[0147] As noted above, the reflection optical fibre and excitation optical fibre may be connected through an optical splitter.

[0148] Excitation light source

[0149] The excitation light source produces excitation light for irradiating the semiconductor wafer.

[0150] The excitation light source is preferably a laser.

[0151] The inventors have identified various considerations which should be made when choosing the wavelength or range of wavelengths that the excitation light source should produce.

[0152] The wavelength or range of wavelengths of the excitation light must stimulate emission of Raman scattered light, and in the case of the first aspect also photoluminescence emission from the semiconductor wafer.

[0153] It is desirable that the wavelength or range of wavelengths of the excitation light is selected such that it enhances the intensity of the Raman scattered light signal. Raman scattered light signals increase in intensity with the fourth power of the frequency of the excitation light and so the wavelength of the excitation light may be chosen with this in mind.

[0154] It is also desirable that the wavelength or range of wavelengths of the excitation light is selected so that the excitation light has an energy which is close to the energy of the bandgap of the material from which the semiconductor wafer is made. For example, silicon has a bandgap of about 1 .12 eV, which corresponds to a wavelength of about 1100 nm. If the application of the present invention involves measuring the temperature of a silicon wafer, then it desirable that the wavelength of the excitation light is close to 1100 nm.

[0155] For measuring the temperature of certain semiconductor wafers it is also desirable that the wavelength or range of wavelengths of the excitation light is selected to avoid regions of the spectrum for which the semiconductor wafer is substantially transparent, since the Raman signal and photoluminescence signal generated by such wavelengths will be low in this region.

[0156] It is also desirable that the wavelength of the excitation light is selected to be different from the wavelengths emitted by a heater which may be present for illuminating the semiconductor wafer. This means that the detection system may be configured to detect a range of wavelengths which includes the elastically scattered light and reflected excitation light from the sample while not including spurious signals arising from the heater. This is advantageous in those embodiments of the present invention where, when calibrating an equation relating temperature to the photoluminescence emission signal, the photoluminescence emission signal is normalised to either an elastically scattered light signal or a reflected light signal. In these embodiments, the extent of noise arising from spurious signals from the heater is reduced when detecting the elastically scattered light signal or reflected light signal.

[0157] Taking these considerations into account:

[0158] The excitation light source may produce excitation light having a maximum intensity at a wavelength or range of wavelengths no less than 200 nm, no less than 250 nm, no less than 300 nm, no less than 350 nm, no less than 400 nm, no less than 450 nm, no less than 500 nm, no less than 550 nm, no less than 600 nm, no less than 650 nm, no less than 700 nm, no less than 750 nm, or no less than 785 nm.

[0159] The excitation light source may produce excitation light having a maximum intensity at a wavelength or range of wavelengths no more than 1500 nm, no more than 1400 nm, no more than 1300 nm, no more than 1200 nm, no more than 1100 nm, no more than 1000 nm, no more than 950 nm, no more than 900 nm, no more than 850 nm, no more than 800 nm, no more than 750 nm, no more than 700 nm, no more than 650 nm, no more than 600 nm, no more than 550 nm, no more than 500 nm, and no more than 450 nm.

[0160] Preferably, the excitation light source produces light having a maximum intensity in a wavelength range of 200 nm to 1500 nm, preferably 400 nm to 1200 nm, and more preferably 450 nm to 850 nm.

[0161] The excitation light source may produce excitation light having a maximum intensity at a wavelength of 450 nm, or 470 nm, or 532 nm, or 785 nm.

[0162] When the semiconductor wafer is made from silicon, the excitation light source may preferably produce excitation light having a maximum intensity at a wavelength of 785 nm.

[0163] Preferably, the excitation light source is a narrow-linewidth or single-frequency laser.

[0164] Preferably, the thermometry device incorporates an excitation light filter (xiii) to increase the monochromaticity of the light source. In particular, the present inventors have found that side-modes emitted from lasers can complicate detection of Raman signal, and thus that it is advantageous to use an excitation light filter to reduce those side-modes and potentially decrease linewidth of the main emission wavelength.

[0165] Optionally, the excitation light source includes a modulator. The modulator may, for example, modulate the excitation light source to introduce a characteristic frequency to the detected Stokes and anti-Stokes signal. The modulation of the signal can then be demodulated (e.g. by a lock-in amplifier) so that signal within a specific frequency region around the modulation frequency is separable from background noise (e.g. amplified spontaneous emission “ASE” background, or sidebands of other origin).

[0166] Wafer processing apparatus

[0167] The present invention also comprises wafer processing apparatus, for treating a semiconductor wafer, incorporating a thermometry device as described above.

[0168] Suitably, such apparatus comprises: a treatment chamber; a wafer support for holding a semiconductor wafer; and a thermometry device for measuring the temperature of a semiconductor wafer positioned on the wafer support, the thermometry device being as defined above.

[0169] In particular, the present invention provides apparatus for treating a semiconductor wafer, the apparatus comprising: a treatment chamber; a wafer support for holding a semiconductor wafer; and a thermometry device for measuring the temperature of a semiconductor wafer positioned on the wafer support, the thermometry device comprising: an excitation light source for irradiating a semiconductor wafer held on the wafer support, wherein in use irradiation of the semiconductor wafer stimulates emission of a Raman scattered light signal and a photoluminescence emission signal; a detection system configured to detect a Raman scattered light signal and photoluminescence signal emitted from a semiconductor wafer held on the wafer support; and a processor configured to determine a Raman-derived temperature of the semiconductor wafer from information relating to the Raman scattered light signal, and calibrate an equation relating temperature to the photoluminescence emission signal based on the Raman-derived temperature to obtain a calibrated equation, and measure the temperature of the semiconductor wafer from the calibrated equation.

[0170] The processor of the apparatus is configured to calibrate the photoluminescence emission signal from a semiconductor wafer with the Raman scattered light signal from a semiconductor wafer in such a way as to overcome drawbacks associated with the use of photoluminescence emission signals and Raman scattered light signals individually for measuring the temperature of a semiconductor wafer.

[0171] The apparatus may operate in a “top surface” implementation, or in a “bottom surface” implementation. In a “top surface” implementation, the wafer is illuminated on a “top surface” which is distal to the wafer support and signal is detected from that surface. In a “bottom surface” implementation, the wafer is illuminated on a “bottom surface” which is proximal to, and optionally in contact with, the wafer support and signal is detected from that surface.

[0172] Preferably, the wafer processing apparatus of this aspect incorporates an autofocus system as described above.

[0173] In addition, a further aspect of the present invention provides wafer processing apparatus for treating a semiconductor wafer, the apparatus comprising: a treatment chamber; a wafer support for holding a semiconductor wafer; and a thermometry device for measuring the temperature of a semiconductor wafer positioned on the wafer support, the thermometry device comprising: an excitation light source for irradiating a semiconductor wafer held on the wafer support with a focussed excitation light to stimulate emission of Raman scattered light signal from the semiconductor wafer; a detection system configured to detect a Raman scattered light signal and photoluminescence signal emitted from a semiconductor wafer held on the wafer support; and an autofocus system to monitor the focal position of the excitation light source and adjust the focal position to optimise the detected Raman scattered light signal.

[0174] Wafer Support

[0175] The wafer support may be a chuck. Preferably, the chuck may be a rotatable chuck which includes a chuck body which is rotatably mounted on a base. The chuck body is rotatable relative to the base about a rotational axis. Rotation of the chuck body relative to the base may be driven, for example, by a motor, which may itself be controlled by a controller. The chuck body may include grippers which are adapted to receive a wafer and hold the wafer securely in place. In this manner, when a wafer is mounted on the rotatable chuck via the gripping means, the wafer may be rotated by rotating the chuck body. In some embodiments, the grippers are gripping pins which exert a gripping force to hold the wafer in place. However, other suitable mechanisms may be used for holding the wafer in place instead, including but not limited to a clamp, screws, and a suction holder.

[0176] The chuck may include a transparent plate mounted on the chuck body. The transparent plate can be made of any suitable transparent material, for example quartz or sapphire. The transparent plate may be secured to the chuck body, such that when the chuck is a rotatable chuck the transparent plate rotates with the chuck body relative to the base. The transparent plate may be arranged such that it is substantially parallel to the wafer when the wafer is mounted on the chuck.

[0177] Heater

[0178] Preferably, the wafer processing apparatus comprises a heater configured to heat a semiconductor wafer held on the wafer support. There are various applications for which it is necessary or useful to heat the semiconductor wafer. For example, for applications involving dispensing a liquid onto a semiconductor wafer it is often necessary or useful to provide a heater to evaporate the liquid from the surface of the semiconductor wafer.

[0179] An advantage of the present apparatus is that it enables the temperature of a sample to be accurately measured from a narrow range of detected wavelengths corresponding to Raman scattered light signals and photoluminescence emission signals, wherein the range of detected wavelengths is substantially disparate from the wavelengths of light emitted by the heater. This means that detector interference caused by spurious signals arising from the heater is reduced in the present apparatus, which allows the temperature of a sample to be measured accurately while the heater is in operation.

[0180] Another advantage of those embodiments of the apparatus which comprise a heater and an autofocus system for certain applications is that the autofocus system can automatically focus the Raman scattered light signal and / or the photoluminescence emission signal from a semiconductor wafer, wherein the optical path length of excitation light between the excitation light source and the semiconductor wafer is changeable due to evaporation of liquid dispense on the semiconductor wafer when the heater is in operation.

[0181] Preferably, the heater is arranged to be on an opposite side of the semiconductor wafer compared to the excitation light irradiating the semiconductor wafer.

[0182] It is desirable that the heater is arranged on a side of the semiconductor wafer so that it can substantially uniformly heat the plane surface of the semiconductor wafer. It is advantageous that the heater is arranged on an opposite side of the semiconductor wafer compared to the excitation light so that the heater does not obstruct excitation light from the excitation light source.

[0183] In some embodiments of the apparatus, the heater comprises an array of light-emitting heating elements.

[0184] It is desirable that the heater comprises an array of heating elements so that the heater may cover an area which is substantially the same as the semiconductor wafer to ensure that the semiconductor wafer is substantially uniformly heated.

[0185] Light-emitting heating elements are desirable as radiative heating is a non-contact mechanism of heating and so does not perturb the semiconductor wafer.

[0186] An advantage of the present apparatus is that it enables the temperature of a sample to be accurately measured from a narrow range of detected wavelengths corresponding to Raman scattered light signals and photoluminescence emission signals. In particular, the range of detected wavelengths may be different to the wavelength(s) of light emitted by the heating elements. This means that detector interference caused by spurious signals arising from the heating elements is reduced in the present apparatus, which allows the temperature of a sample to be measured accurately while the heater is in operation.

[0187] In some embodiments of the apparatus, the light-emitting heating elements are light-emitting diodes configured to emit light having a predetermined wavelength, or wavelengths within a predetermined range of wavelengths.

[0188] Preferably, the wavelength range emitted by the light-emitting heating elements is different to the wavelength of the excitation light source, Raman scattered light signal, and the photoluminescence emission signal. This reduces detector interference caused by spurious signals arising from the light-emitting diodes, which allows the temperature of a sample to be measured accurately while the heater is in operation.

[0189] Preferably, the light-emitting heating elements are light-emitting diodes configured to emit light having a single predetermined wavelength. The light-emitting diodes may be configured to emit light having a predetermined wavelength which is no shorter than 350 nm, no shorter than 500 nm, no shorter than 750 nm, or 1000 nm.

[0190] The light-emitting diodes may be configured to emit light having a predetermined wavelength which is no less than 380 nm and no more than 980 nm, or no less than 450 nm and no more than 720 nm, or no less than 660 nm and no more than 760 nm, or no less than 840 nm and no more than 980 nm. The inventors have found that these wavelength ranges are particularly suitable for heating a semiconductor wafer.

[0191] Preferably, the light-emitting diodes are configured to emit light having a predetermined wavelength which is at least 200 nm, at least 100 nm, or at least 50 nm apart from the Raman scattered light signal and photoluminescence emission signal wavelengths.

[0192] It is desirable that the predetermined wavelength emitted by the light-emitting diodes has no or minimal overlap with the wavelengths emitted from the semiconductor wafer. In particular, it is preferable that the wavelength emitted by the light-emitting diodes has no or minimal overlap with the Raman scattered light signal and the photoluminescence emission signal emitted from the sample. For example, the signal intensity from the light-emitting diodes may be no more than 10%, no more than 5%, or no more than 2% of the intensity of the Raman signal at any position of overlap between the wavelengths of the signal emitted from the light-emitting diodes and the Raman signal. It is also desirable that the predetermined wavelength emitted by the light-emitting diodes has no or minimal overlap with the wavelength of the excitation light.

[0193] The light-emitting heating elements may also be white light-emitting diodes which each emit light comprising a plurality of wavelengths in the visible light spectrum.

[0194] Advantageously, the white light-emitting diodes may emit light having a relatively low optical power in a wavelength region close to the wavelength of the Raman scattered light signal and / or the photoluminescence emission signal. For example, the optical power of the white light-emitting diodes may be less than 5%, less than 4%, less than 3%, less than 2%, less than 1%, or less than 0.5% of the total optical power at wavelengths longer than 750 nm, or longer than 720 nm, or longer than 700 nm.

[0195] When the semiconductor wafer is supported on a chuck, the chuck is preferably substantially transparent to wavelengths of light emitted by the heater. “Transparent” is taken to mean that all or a majority of light emitted by the heater, the light-emitting heating elements, or the light-emitting diodes is transmitted through the transparent plate.

[0196] Fluid delivery system

[0197] Optionally, the wafer processing apparatus comprises a fluid delivery system for dispensing a fluid (gas and / or liquid) onto a semiconductor wafer.

[0198] Those embodiments of the present apparatus which comprise a rotatable chuck and a fluid delivery system are particularly advantageous, as the rotatable chuck can rotate a semiconductor wafer supported on the chuck, which substantially homogeneously disperses a fluid dispensed onto the semiconductor wafer by the fluid delivery system.

[0199] An advantage of those embodiments of the apparatus which comprise a fluid delivery system and an autofocus system is that the autofocus can automatically focus the Raman scattered light signal and / or the photoluminescence emission signal from a semiconductor wafer before and after fluid is dispensed onto the semiconductor wafer, which can change the optical path length of excitation light between the excitation light source and the semiconductor wafer. This allows the temperature of the semiconductor wafer to be accurately measured before and after fluid is dispensed on the semiconductor wafer without requiring any sophisticated or time-consuming calibration or baseline temperature measurement steps to be completed between measurements.

[0200] An advantage of those embodiments of the present apparatus which comprise a fluid delivery system, a heater and an autofocus system is that the autofocus system can automatically focus the Raman scattered light signal and / or the photoluminescence emission signal from a semiconductor wafer before, after, and during the evaporation of a fluid dispense dispensed onto the semiconductor wafer while the semiconductor wafer is heated. The optical path length of excitation light between the excitation light source and the semiconductor wafer is changeable as fluid dispense dispensed on the semiconductor wafer evaporates. The provision of the autofocus system means that the temperature of the semiconductor wafer can be measured accurately while the fluid dispense evaporates from the semiconductor wafer.

[0201] An advantage of those embodiments of the present apparatus which comprise a fluid delivery system, a rotatable chuck and an autofocus system is that the autofocus system can automatically focus the Raman scattered light signal and / or the photoluminescence emission signal from a semiconductor wafer before, after, and during the dispersion of the fluid dispense substantially homogeneously onto the surface of the semiconductor wafer. The optical path length of excitation light between the excitation light source and the semiconductor wafer is changeable as fluid dispense is dispensed and dispersed onto the semiconductor wafer. The provision of the autofocus system means that the temperature of the semiconductor wafer can be measured accurately while the fluid dispense is dispensed and dispersed substantially homogeneously on the surface of the semiconductor wafer.

[0202] ***

[0203] 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.

[0204] 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.

[0205] 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. Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0206] 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.

[0207] 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%.

[0208] The various aspects of the invention are illustrated in accompanying Figures 1 to 14.

[0209] Figures 1 and 2 shows an example of apparatus 10 used to carry out the method of the present invention. The apparatus includes a chamber 51 housing a rotary chuck 12. A semiconductor wafer 1 is attached to the surface of the rotary chuck 12 through a suitable mechanism, in this case through the use of gripping pins 13. Suitable examples of gripping pins are shown and described in earlier application US 2018 / 0047593. The surface 14 of the rotary chuck 12 is transparent, and a heater 15 is arranged under the surface 14. In this case, the heater 15 includes a plurality of light emitting diodes (LEDs) arranged in one or more radial zones to allow radial heating of the substrate 1. The heater can be operated to provide a moving heat wave that moves from a central location of the substrate outwardly to a radially outer edge thereof as the rotary chuck 12 rotates. Suitable examples of a rotary chuck performing radial heating of a substrate are shown and described in US 2018 / 0047593.

[0210] The rotary chuck 12 is rotated by chuck rotating motor 16 via a drive shaft 17 as shown. In other examples, the motor 16 includes a rotor and stator and the rotor is driven magnetically without physical contact. Suitable examples are shown in US 6,485,531 . In a first step, a first rinsing liquid is delivered to the rotating substrate 1 by a liquid dispense 21 and a nozzle 22. A valve 24 selectively supplies the rinsing liquid from a liquid supply 20 to the liquid dispense 21 . The liquid dispense 21 and nozzle 22 are scanned across the substrate 1 by liquid dispense motor 23, to ensure that all regions of the substrate are treated. Liquid spun off of the substrate 1 is collected by first liquid collector 54 circumferentially surrounding the chuck 12, from where it is removed via drain 57. Gas from the interior of the first liquid collector 54 (in particular, mist generated by spun liquid impacting the liquid collector) is removed by exhaust 56. Suitable examples of the liquid collecting apparatus are shown in earlier patent EP 1 609 172 B.

[0211] Next, chuck 12 is raised along its rotation axis within housing 51 to a second position by chuck raising motor 18. The rinsing procedure is then carried out with a second liquid, with liquid spun off into second liquid collector 55 and removed by a separate liquid drain and gas exhaust.

[0212] After rinsing is complete, the liquid dispense motor 23 rotates liquid dispense 21 away from the surface of the substrate 1 , into an inactive position, and the gas dispense motor 33 rotates gas dispense 31 into position above the substrate. This is shown in greater detail in Figure 2, in which liquid liquid dispense 21 has been rotated into an inactive position, and gas dispense 31 has been rotated into a position above the substrate 1. The gas dispense delivers a gaseous mixture of nitrogen from gas supply 30 to nozzle 34 via control valve 32. In this embodiment, the horizontal position of the nozzle 34 is adjusted by gas dispense motor 33, so as to scan the nozzle across the surface of the rotating substrate 1 , generally from the centre outwards. The action of the motors and the various valves is coordinated by controller 40.

[0213] During processing, a fan 52 provides a continuous supply of air to the chamber 51 . To avoid pressure build up in the chamber 51 , air inserted through the fan filter unit is exhausted through exhausts 56 and, to a lesser extent, through vent 53.

[0214] The apparatus shown in Figures 1 and 2 includes thermometry device 100 according to the present invention. The thermometry device 100 incorporates an excitation light source 110 which directs excitation light of 785 nm to a probe head 120 via an optical fibre. Focussed excitation light 111 exits the probe head via an objective lens and is focussed onto semiconductor wafer 1. Raman and photoluminescence signal emitted by the semiconductor wafer 1 passes back into probe head 120, where it is directed to detector unit 130 via a further optical fibre. To ensure that the focussed excitation light 111 remains focussed on the semiconductor surface, the thermometry device 100 incorporates an autofocus system in which elastically reflected light returning to the probe head is directed to autofocus unit 140, which adjusts the vertical position of probe head 120 via voice coil actuator 141 so as to maximise the intensity of the elastically reflected light received at the autofocus unit 140. The probe head is mounted to the treatment chamber 51. This autofocus unit 140 is also able to adjust the focus as the chuck 12 is raised between treatment steps and is able to account for changes in optical path length caused when liquid is dispensed from nozzle 22 onto the semiconductor wafer 1.

[0215] In this case, the thermometry device 100 has been retrofitted to apparatus 10. In particular, the probe head 120 has been fixed to the inside wall of treatment chamber 51 , with the excitation light source 110, detector unit 130 and autofocus unit 140 positioned outside the treatment chamber 51. The optical fibres to the probe head and electrical connection (not shown) to the voice coil actuator 141 passing through a small hole drilled in the treatment chamber.

[0216] The thermometry device 100 is shown in more detail in Figure 3, which better illustrates the interconnection between components of the device.

[0217] In particular, Figure 3 shows that excitation light source 110 delivers excitation light to probe head 120 via optical fibre 112 and optical fibre 113, and autofocus unit 140 receives reflected light back along optical fibre 113 and optical fibre 142. An optical splitter 143 is used to connect optical fibre 113 to both optical fibre 112 and optical fibre 142. In this arrangement, excitation light travels efficiently down optical fibre 112 and optical fibre 113 via optical splitter 143, with minimal introduction of excitation light down optical fibre 142. In contrast, reflected light returning from probe head 120 along optical fibre 113 is split between optical fibre 112 and optical fibre 142.

[0218] Detector unit 130 is also connected to probe head 120 via a detection optical fibre 131.

[0219] Computer 150 receives signals from detector unit 130 relating to Raman signal intensity and photoluminescence signal intensity, and uses this to determine the temperature of semiconductor wafer 1. Computer 150 also receives signals from autofocus unit 140 relating to the intensity of reflected light from the semiconductor wafer 1 , and delivers control instructions to voice coil actuator 141 via electrical connection 151 so as to maximise the amount of reflected light detected, and thereby ensure that excitation light 111 is optimally focussed at the surface of semiconductor wafer 1 .

[0220] Figure 4 provides a more detailed internal view of probe head 120. Optical fibre 113 is attached to a tube housing 207 via SMA connector 201 . Divergent light (shown with diagonal hatching) exiting the optical fibre 113 is collimated using collimating lens 203, passes through a bandpass filter 205 to remove unwanted wavelengths (such as fluorescence introduced by optical fibre 113), and enters objective lens 211 via beamsplitter 209. The objective lens is a high numerical aperture lens (in this case, having an NA of 0.7) which tightly focusses excitation light onto the semiconductor wafer. Raman signal and photoluminescence signal from the semiconductor wafer is collected by objective lens 211 , and is reflected at beam splitter 209. The signal (shown in wavy hatching) passes through notch filter 213, and is focussed into detection optical fibre 131 using lens 217. To achieve a secure and stable alignment of the components, collimating lens 203 and bandpass filter 205 have an external thread which can be screwed into an internal thread provided within tube housing 207. Likewise, tube housing 215 has an internal thread into which are screwed the notch filter 213, and lens 217, with the detection optical fibre 131 attached to the end of the tube housing 215 via an SMA connector 219.

[0221] Voice-coil actuator 141 is securely fixed to the side of the probe head. As can be seen, movement of the probe head via actuator 141 allows the focal plane of the objective lens to be moved whilst preserving alignment of all other optical components.

[0222] Figure 5 provides a more detailed internal view of detection unit 130. Detection optical fibre 301 is attached to detector unit 130 via SMA connector 303. Divergent light exiting the fibre is collimated using collimating lens 305, before being filtered using notch filter 307, and spectrally dispersed using grating 309 so as to allow detection of a wavelength spectrum. The dispersed light is then focussed onto CMOS array detector 313 using lens 311.

[0223] As can be seen, the emission signal is filtered both before and after the detection optical fibre 131 by notch filter 213 and notch filter 307 respectively. Notch filter 213 helps to clean the emission signal so as minimise the production of fluorescence within the optical fibre, and notch filter 307 helps to suppress signal from any fluorescence generated within the optical fibre.

[0224] Figure 6 shows an example of anti-Stokes (AAS) and Stokes (As) Raman background- corrected signal generated from a silicon wafer using a thermometry device in accordance with the invention, positioned either side of a central peak corresponding to the contribution from excitation light. As can be seen, the anti-Stokes peak is considerably smaller than the Stokes peak. The small size of the anti-Stokes peak means that the SNR of this peak is also considerably lower than that for the Stokes peak.

[0225] Figure 7 shows variation of the detected anti-Stokes peak from a silicon wafer as temperature is increased. The peak grows and shifts to lower wavenumber as the temperature is increased. Figure 8 shows variation of the detected Stokes peak from a silicon wafer as temperature is increased. In contrast to the anti-Stokes peak, the Stokes peak shrinks as the temperature is increased and shifts to lower wavenumber.

[0226] Figure 9 is a plot showing the ratio of the area of the anti-Stokes peak compared to the Stokes peak across a range of temperatures, for two sets of experiments carried out on a silicon wafer. In both cases, there is a clear linear relationship between the ratio between 25°C and 100°C. This relationship can be fitted in a straight-line plot using the equation T^ a^ + b.

[0227] In Figure 10, the same procedure was carried out but across 10 different spots on a silicon wafer. The results show very consistent values obtained for all different positions of the wafer, and were consistent with variation in values obtained for repeated measurement of the same spot. The uncertainty in the measurements corresponded to around ± 2.5°C across all temperatures tested.

[0228] Figure 11 shows measurement of the ratio of anti-Stokes to Stokes peaks for a range of different wafers, in particular, wafers bearing different hard mask layers. Measured wafers include a bare single crystal silicon wafer (Si), a doped single crystal silicon wafer (doped Si), a polycrystalline silicon (Poly Si), a single crystal silicon wafer bearing a patterned surface (special structured silicon), as well as single crystal silicon wafers bearing different hard mask layers on their surface, including a wafer bearing a thermal oxide layer (ThOx), titanium nitride layer (TiN), liquid phase chemical vapour deposition silicon nitride (LPCVDSiNx), silicon oxide hard mask (SiOxHM), and atomic layer deposition silicon nitride (ALDSiNx) layer. The results show the linear relationship between temperature and the ratio of the anti-Stokes and Stokes Raman signals of each of the measured wafers, and that the relationship between this ratio and temperature is relatively unaffected by surface treatments. In particular, the values for the ThOx, Si, LPCVDSiNx, special structured wafer, doped Si and ALDSiNx wafers overlap, such that the same coefficients a and b in calibrated equation (i) can be used to relate temperature to Raman signal.

[0229] Figure 12 is a plot showing a calibration of equation (i) using a SensArray® (SA) wafer mounted with an infrared thermal sensor. The results show the temperature of the wafer at intervals of about 10 °C between approximately 60 °C and 120 °C and subsequently down from approximately 120 °C to approximately 90 °C. The temperature of the wafer was measured at each period over a period of approximately 30 seconds to evaluate the stability of the Raman-measured temperature reading. The wafer temperature is measured using the infrared thermal sensor and compared to the temperature according to equation (i) measured by the Raman sensor. The results show that the Raman-measured temperature is highly accurate and responds quickly to both increases and decreases in the temperature of the semiconductor wafer. The Raman-measured temperature is accurate across the full measured temperature range of <60 °C to <120 °C and displays excellent stability at each of the measured temperature intervals.

[0230] Figure 13 is a plot showing time-course temperature measurements conducted without using an autofocus or manual focus corrections, to show the effects of drift on accuracy of temperature measurement. Measurements were conducted on a Si wafer and collected at 50 °C, 60 °C, 70 °C, and 80 °C to evaluate the accuracy and stability of the temperature reading at different temperatures. Measurements were collected at each temperature interval for at least 45 seconds, and up to several minutes, to evaluate the stability of the temperature measurements. The data show the measured temperatures of the wafers (solid lines) at known reference temperatures (dash-and-dot lines) and additionally the converted (though not calibrated) photoluminescence signal (dotted line). The photoluminescence signal was not calibrated to match the Raman temperature in order to allow the general trends in behaviour to be observed when plotted on the same graph. The results show that, in the absence of any automatic or manual focus correction, the measured temperature can drift over time. The test setup with a clamped wafer resulted in increased wafer bow (as Si expansion is hindered by the clamping mechanism) which increases the sensor to wafer distance. This explains the higher deviation as well at higher temperatures. At higher temperatures such as 70 °C and 80 °C this decline is particularly evident. The results also show that the initial temperature measurement after ramping between temperature intervals may be inaccurate without any autofocus or manual focus correction.

[0231] Figure 14 is a plot showing the measured temperature of a wafer as a function of the position of the semiconductor wafer in relation to its focal point. Measurements were performed at numerical apertures of 0.16 (NA016), 0.30 (NA030), 0.54 (NA054), and 0.70 (NA070). Measurements were conducted on a Si wafer at various known reference temperatures. The temperature is calibrated to be precisely determined at Delta Focalpoint = 0 in each case, with multiple measurements to ensure accuracy (note that this calibrated temperature was different across different numerical apertures, due to the wafer being held at different temperatures for different numerical apertures). The results show that the measured temperature remains relatively stable as the semiconductor wafer is moved out of focus, in particular at lower numerical apertures. For example, measurements at a numerical aperture of 0.16 fluctuated by only approximately ±3 °C as the focal point was adjusted by ±300 pm. In general the measured temperature tended towards a lower value as the focal point increased and to a higher value as the focal point decreased.

Claims

CLAIMS1 . A method of measuring the temperature of a semiconductor wafer, using a thermometry device comprising an excitation light source, a detection system, and an autofocus system, the method comprising the steps of: irradiating the semiconductor wafer with a focussed excitation light source to stimulate emission of a Raman scattered light signal from the semiconductor wafer; detecting the Raman scattered light signal emitted from the semiconductor wafer using the detection system; determining a Raman-derived temperature of the semiconductor wafer from information relating to the Raman scattered light signal; and using the autofocus system to monitor the focal position of the excitation light source and adjusting the thermometry device so as move the focal position to optimise the detected Raman scattered light signal.

2. A method of measuring the temperature of a semiconductor wafer, using a thermometry device comprising an excitation light source and a detection system, the method comprising steps of: irradiating the semiconductor wafer with the excitation light source to stimulate emission of a Raman scattered light signal from the semiconductor wafer and a photoluminescence emission signal from the semiconductor wafer; simultaneously detecting the Raman scattered light signal and photoluminescence signal emitted from the semiconductor wafer using the detection system; determining a Raman-derived temperature of the semiconductor wafer from information relating to the Raman scattered light signal; deriving a calibrated equation relating temperature to the photoluminescence emission signal based on the Raman-derived temperature; and carrying out a further measurement of the photoluminescence signal and determining the temperature of the semiconductor based on the calibrated equation.

3. A method according to claim 2, wherein the thermometry device further comprises an autofocus system to monitor the focal position of the excitation light source and adjust the apparatus so as move the focal position to optimise the detected Raman scattered light signal.

4. A method according to claim 1 or 3, wherein monitoring the focal position involves monitoring the intensity of excitation light reflected from the semiconductor wafer.

5. A method according to any one of claims 1 , 3 or 4, wherein the excitation light is focussed onto the semiconductor wafer using via an objective lens, and wherein adjusting the thermometry device so as move the focal position to optimise the detected Raman scattered light signal comprises moving the objective lens relative to the semiconductor wafer.

6. A method according to any one of the preceding claims, wherein the thermometry device operates in a confocal modality.

7. A method according to claim 6, wherein the excitation light source is focussed onto the semiconductor surface, and the detection system include an emission lens to focus detected emission through an aperture positioned in an optically conjugate plane to reject out-of-focus light.

8. A method according to claim 7, wherein the detection system includes a detection optical fibre, and the aperture is provided by the face of the detection optical fibre.

9. A method according to any one of the preceding claims, wherein the thermometry device comprises: i. said excitation light source; ii. an excitation optical fibre for receiving light from the excitation light source;Hi. a collimating lens, for collimating the excitation light source exiting the excitation optical fibre; iv. an objective lens, to focus the excitation light into a focal plane positioned at the semiconductor wafer; v. a detection optical fibre to collect emitted signal from the semiconductor wafer, the detection optical fibre having an end face; vi. an emission lens for focussing the emitted signal onto the end face of the detection optical fibre; and vii. a beamsplitter, to separate excitation light from emitted signal.

10. A method according to any one of claims 1 or 3 to 8, wherein the thermometry device comprises: an excitation light source; optionally, an excitation light filter;an excitation optical fibre for receiving light from the excitation light source; a collimating lens, for collimating the excitation light exiting the excitation optical fibre; an objective lens, to focus the excitation light into a focal plane positioned at the semiconductor wafer; a detection optical fibre to collect emitted signal from the semiconductor wafer, the detection optical fibre having an end face; an emission lens for focussing the emitted signal onto the end face of the detection optical fibre; a beamsplitter, to separate excitation light from emitted signal;- wherein the excitation optical fibre, collimating lens, objective lens, detection optical fibre, emission lens and beamsplitter are mounted on or within a probe head; an actuator attached to the probe head; a detection system comprising: a detector; a dispersive element for spectrally separating wavelengths ahead of the detector; optionally, an emission filter; an autofocus system, comprising: a reflection optical fibre, for receiving reflected excitation light from the semiconductor wafer; a sensor for measuring the intensity of the reflected excitation light from the reflection optical fibre; and a processor to actuate the actuator attached to the probe head in response to the intensity of the reflected excitation light from the reflection optical fibre.11 . A method according to claim 2 or 3, wherein the step of calibrating the equation relating temperature to the photoluminescence emission signal comprises taking / Raman- derived temperatures, Tl hand inputting into equation (1):wherein / is an integer greater than or equal to 2, L, is the intensity of the photoluminescence emission signal, Xtis the intensity of at least one of a Stokes signal obtained from the information relating to the Raman scattered light signal, an elastically scattered light signalemitted from the semiconductor wafer, and a reflected light signal reflected from the semiconductor wafer, and wherein resolving equation (1) determines calibration coefficients a and / ?.

12. The method according to claim 11 , wherein the photoluminescence emission signal is normalised based on the Stokes signal obtained from the information relating to the Raman scattered light signal.

13. The method according to any one of the preceding claims, wherein the excitation light source produces light having a maximum intensity in a wavelength range of 450 nm to 850 nm.

14. The method according to any one of the preceding claims, wherein the detection system comprises a single detector.

15. Apparatus for treating a semiconductor wafer, the apparatus comprising: a treatment chamber; a wafer support for holding a semiconductor wafer; and a thermometry device for measuring the temperature of a semiconductor wafer positioned on the wafer support, the thermometry device comprising: an excitation light source for irradiating a semiconductor wafer held on the wafer support with a focussed excitation light to stimulate emission of Raman scattered light signal from the semiconductor wafer; a detection system configured to detect a Raman scattered light signal emitted from a semiconductor wafer held on the wafer support; and an autofocus system to monitor the focal position of the excitation light source and adjust the focal position to optimise the detected Raman scattered light signal.

16. Apparatus for treating a semiconductor wafer, the apparatus comprising: a treatment chamber; a wafer support for holding a semiconductor wafer; and a thermometry device for measuring the temperature of a semiconductor wafer positioned on the wafer support, the thermometry device comprising:an excitation light source for irradiating a semiconductor wafer held on the wafer support with a excitation light to stimulate emission of Raman scattered light signal from the semiconductor wafer; a detection system configured to detect a Raman scattered light signal and photoluminescence signal emitted from a semiconductor wafer held on the wafer support; and a processor configured to determine a Raman-derived temperature of the semiconductor wafer from information relating to the Raman scattered light signal, and derive a calibrated equation relating temperature to the photoluminescence emission signal based on the Raman-derived temperature, and measure the temperature of the semiconductor wafer from the calibrated equation.

17. Apparatus according to claim 16, wherein the apparatus further comprises an autofocus system to monitor the focal position of the excitation light source and adjust the focal position to optimise the detected Raman scattered light signal.

18. Apparatus according to any one of claims 15 to 17, further comprising a heater configured to heat a semiconductor wafer held on the wafer support.

19. Apparatus according to claim 18, wherein the heater is arranged to be on an opposite side of the semiconductor wafer compared to the excitation light excitation light in use.

20. Apparatus according to claim 18 or 19, wherein the heater comprises an array of light-emitting heating elements.21 . Apparatus according to claim 20, wherein the light-emitting heating elements are light-emitting diodes configured to emit light having a predetermined wavelength.

22. Apparatus according to claim 20, wherein the predetermined wavelength emitted by the light-emitting diodes has no or minimal overlap with the wavelengths of the emitted signal form the semiconductor wafer.

23. Apparatus according to any one of claims 15 to 22, further comprising a fluid delivery system for dispensing a fluid onto a semiconductor wafer.

24. A thermometry device comprising: an excitation light source; optionally, an excitation light filter; an excitation optical fibre for receiving light from the excitation light source;a collimating lens, for collimating the excitation light exiting the excitation optical fibre; an objective lens, to focus the excitation light into a focal plane positioned at a semiconductor wafer in use; a detection optical fibre to collect emitted signal from a semiconductor wafer in use, the detection optical fibre having an end face; an emission lens for focussing the emitted signal onto the end face of the detection optical fibre; a beamsplitter, to separate excitation light from emitted signal;- wherein the excitation optical fibre, collimating lens, objective lens, detection optical fibre, emission lens and beamsplitter are mounted on or within a probe head; an actuator attached to the probe head, for moving the probe head relative to a semiconductor wafer in use; a detection system comprising: a detector; a dispersive element for spectrally separating wavelengths ahead of the detector; optionally, an emission filter; and an autofocus system, comprising: a reflection optical fibre, for receiving reflected excitation light from a semiconductor wafer in use; a sensor for measuring the intensity of the reflected excitation light from the reflection optical fibre; a processor to actuate the actuator attached to the probe head in response to the intensity of the reflected excitation light from the reflection optical fibre.

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