GB2474425A

GB2474425A - Method and apparatus for measuring temperature

Info

Publication number: GB2474425A
Application number: GB0917825A
Authority: GB
Inventors: Christopher Hunter Oxley; Richard Henry Hopper
Original assignee: De Montfort University
Current assignee: De Montfort University
Priority date: 2009-10-13
Filing date: 2009-10-13
Publication date: 2011-04-20
Anticipated expiration: 2029-10-13
Also published as: GB2474425B; GB0917825D0; WO2011045558A1

Abstract

A method for measuring the temperature of a first material 10 comprises measuring a temperature-related characteristic of a microparticle, or microsphere, of a second material 12 in thermal contact with the first material 10 and calculating the temperature of the first material 10 using the measured temperature-related characteristic of the microparticle of the second material 12. The temperature related characteristic may be optically detected and may comprise the infrared radiation emitted from the microparticle or the optical phonon activity measured using Raman spectroscopy. The microparticle of the second material 12 may comprise carbon or a semiconductor material and can be located on a surface 10a of the first material 10 in point thermal contact with the surface 10a, thus enabling the measurement of the surface temperature of the first material 10 at the point of contact. A plurality of microparticles may be deposited at discrete locations to provide a temperature profile across a fist material. An apparatus 14 for measuring the surface temperature of the first material 10 is also described.

Description

Method and apparatus for measuring temperature

TECHNICAL FIELD

The present invention relates generally to a method and apparatus for measuring temperature. More particularly, embodiments of the present invention relate to a method for measuring the surface temperature of a first material, for example to permit thermal mapping of the first material. The method is particularly, but not exclusively, suitable for measuring the surface temperature of a semiconductor device. The method can also be used to measure the temperature of a first material in contact with an item, thus permitting the temperature of the item to be determined.

Embodiments of the present invention also relate to apparatus for measuring the temperature of a first material.

BACKGROUND TO THE iNVENTION

Semiconductor materials used in the manufacture of power electronic devices, such as power transistors, can generate significant amounts of heat. This can lead to high operating temperatures, compromising the reliability of such devices. It is, therefore, desirable to be able to accurately measure the operating temperature of semiconductor and other devices (such as microelectromechanical systems (MEMS) and photonic devices).

A number of techniques for measuring the operating temperature of a semiconductor device are currently available, including contact type electrical methods and non-contact type optical methods such as infrared (IR) imaging and Raman spectroscopy.

Whilst all of these known techniques have certain benefits, they all suffer from drawbacks.

Contact-type electrical methods require contact between a measuring element, such as a thermocouple, and the surface of the semiconductor device. Due to the inherent thermal capacity of the measuring element, heat flows into it. The operating temperature of the semiconductor is, thus, altered and the measured temperature is consequently not an indication of the true surface operating temperature of the semiconductor device.

Non-contact type optical methods do not suffer from the same difficulty as contact type electrical methods because there is no contact between a measuring element and the surface of the semiconductor device and hence the operating state of the semiconductor device is unaffected.

The temperature measured using JR imaging does, however, tend to be lower than the actual operating temperature of the semiconductor device and temperatures measured using JR imaging have been found in some circumstances to underestimate the actual device operating temperature by up to 80%. This is believed to be due to the fact that most semiconductor materials are at least partially transparent to JR radiation and/or poor emitters of JR radiation. This can lead to inaccuracies in surface temperature measurement because the detected JR radiation is affected by internal reflections of the radiation and emissions from within the material of the semiconductor device, as well as by background radiation. Whilst JR imaging can be used to measure the surface temperature of metal regions of a semiconductor device, the metal surfaces can be highly reflective to JR radiation which can also lead to temperature measurement inaccuracies.

Furthermore, the spatial resolution that can be achieved using JR imaging is limited by the wavelengths of the JR radiation used and this results in temperature averaging and, hence, a measured temperature which can be lower than the operating temperature of the semiconductor device in some regions. Spatial resolution is, for example, at best limited to approximately 2.5tm. However, many semiconductor devices have features that are in the order of 1 tm or less.

Micro-Raman spectroscopy gives a higher resolution than JR imaging and is therefore capable of providing a more accurate spot temperature. It is, however, difficult to scan over the complete surface of a semiconductor device to enable the surface to be thermally mapped in real-time and there can also be some interaction between the laser photon beam and the semiconductor device which can affect the surface temperature of the semiconductor device. Another problem with Micro-Raman spectroscopy is that it cannot be used to measure the surface temperature of metal regions, such as metal contact and inter-connect metal layers, of a semiconductor device due to the lack of suitable phonon lines in their spectrum.

There is, therefore, a need for a new method and apparatus for measuring temperature that enables the surface temperature of a material to be measured. In particular, there is a need for a new method and apparatus that enables the surface temperature of thin semiconductor material and metal regions of a semiconductor device to be accurately and reliably measured in a substantially non-invasive manner so that the operating state, and hence the operating temperature, of the semiconductor device is not altered.

It would also be desirable to provide a method which enables the temperature of a packaged item to be determined where direct measurement of the temperature of the item is either not possible or undesirable.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provided a method for measuring the temperature of a first material, the method comprising the steps of: (i) measuring a temperature-related characteristic of a microparticle of a second material in thermal contact with the first material; and (ii) calculating the temperature of the first material using the measured temperature-related characteristic of the microparticle of the second material.

According to one particular embodiment of the invention, there is provided a method for measuring the surface temperature of a first material, the method comprising the steps of: (i) measuring a temperature-related characteristic of a microparticle of a second material in point thermal contact with a surface of the first material; and (ii) calculating the surface temperature of the first material using the measured temperature-related characteristic of the microparticle of the second material.

According to a second aspect of the present invention, there is provided a method for measuring the temperature profile across a first material comprising measuring the temperature of the first material at a plurality of locations using the method according to the first aspect of the present invention and generating a temperature profile based on the measured temperatures.

In one particular embodiment, there is provided a method for measuring the surface temperature profile across a surface of a first material comprising measuring the surface temperature of the first material at a plurality of locations using the method according to the first aspect of the present invention and generating a surface temperature profile based on the measured surface temperatures.

According to a third aspect of the present invention, there is provided apparatus for measuring the temperature of a first material, the apparatus comprising: measuring means for measuring a temperature-related characteristic of a microparticle of a second material in thermal contact with the first material; and means for calculating the temperature of the first material using the measured temperature-related characteristic of the microparticle of the second material.

n one particular embodiment, there is provided apparatus for measuring the surface temperature of a first material, the apparatus comprising: measuring means for measuring a temperature-related characteristic of a microparticle of a second material in point thermal contact with a surface of the first material; and means for calculating the surface temperature of the first material using the measured temperature-related characteristic of the microparticle of the second material.

Optional, but sometimes preferred, features of the invention are defined in the dependent claims.

The microparticle of the second material may be located on a surface of the first material. The method may thus include the step of positioning a microparticle of the second material on the surface of the first material.

The microparticle of the second material may alternatively be at least partially, and possibly fully, embedded in the first material. For example, the first material may comprise packaging which encloses an item and which is in contact with the item. In this case, the first material, possibly a plastics material which may be transparent to JR radiation, assumes the same or at least substantially the same temperature as the item it encloses. Thus, by indirectly calculating the temperature of the first material in accordance with method according to the first aspect of the invention, the temperature of the item enclosed by the first material can be indirectly measured. The temperature of the item could, for example, be measured and hence monitored by simply scanning the packaging, containing the item and formed of the first material in which one or more microparticles of the second material are at least partially embedded, under an JR microscopy optical scanner.

As used herein, the term microparticle' refers to particles having a size (major dimension) less than 1OOOtm, with no restriction on lower limit. Jn a similar manner, the term microsphere' is used herein to refer to microparticles which are generally spherical and which have a diameter less than OOOtm, with no restriction on lower limit.

The thermal contact between the first and second materials enables heat to be conducted at the point of contact, or across the area of contact, from the first material into the second material. Accordingly, the temperature of the microparticle of the second material is the same, or substantially the same, as the surface temperature of the first material on whose surface it is located or as the temperature of the first material in which it is at least partially embedded.

In some embodiments in which the microparticte of the second material is located on the surface of the first material, contact between the microparticle of the second material and the surface of the first material is maintained by naturally occurring gravitational, Van der Waals and electrostatic forces occurring between the microparticle and the surface. It is thus possible to manipulate the microparticle of the second material whilst it is in contact with the surface of the first material. For example, in some embodiments, the microparticle of the second material is suitably manipulated to displace it across the surface of the first material. In these embodiments, no form of artificial attachment or bonding is employed to maintain the contact between the microparticle of the second material and the surface of the first material.

In other embodiments, the microparticle of the second material is attached to the surface of the first material. For example, the microparticle of the second material can be bonded to the surface of the first material. The microparticle of the second material could be glued to the surface of a semiconductor device or semiconductor package to enable specific point temperature monitoring for process control.

DRAWINGS

Figure 1 is a diagrammatic illustration of an apparatus for measuring the surface temperature of a first material; and Figure 2 is a graph illustrating the variation of surface temperature across the surface of both semiconductor material and metal contact regions of a semiconductor device measured using the method and apparatus according to embodiments of the present invention and using a known temperature measurement technique.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Embodiments of the present invention will now be described by way of example only, and with reference to the accompanying drawings.

Referring to Figure 1, embodiments of the present invention provide a method for measuring the surface temperature of a first material 10 by measuring a temperature-related characteristic of a second material 12 that is deposited on the surface lOa of the first material 10. The second material 12 is in the form of a microparticle (as hereinbefore defined) and is in point thermal contact with the surface 1 Oa of the first material 10 so that heat can flow, by conduction, from the surface lOa of the first material 10 into the second material 12. This ensures that the temperature of the microparticle of the second material 12 is the same, or substantially the same, as the surface temperature of the first material 10 on which it is deposited.

In typical embodiments, the first material 10 is a material which forms part of a semiconductor device, and the first material 10 may thus comprise semiconductor material and/or a metal.

Semiconductor material is typically at least partially transparent to IR radiation and its actual operating temperature cannot, therefore, be reliably measured using the known JR imaging technique outlined above. In typical embodiments, the first material 10 comprises a thin planar section, commonly referred to as a wafer, of semiconductor material that is substantially transparent to JR radiation. Examples of such semiconductor material include silicon (Si), gallium arsenide (GaAs) and gallium nitride (GaN). Other semiconductor materials, including doped semiconductor materials, are, of course, entirely within the scope of the present invention.

The surface temperature of metal regions, such as metal contacts and metal inter-connect layers, of a semiconductor device cannot be reliably measured using the known JR imaging technique outlined above and cannot be measured at all using the outlined Micro-Raman Spectroscopy technique.

Embodiments of the present invention employ the deposited microparticle of the second material 12 to permit indirect measurement of the temperature of the surface 1 Oa of the first material 10 by measuring a temperature-related characteristic of the second material 12, and the second material 12 can thus be selected so that an appropriate temperature-related characteristic of the second material 12 can be measured using any suitable technique. Such indirect temperature measurement is possible because, as indicated above, the temperature of the deposited microparticle of the second material 12 is the same, or substantially the same, as the temperature of the surface lOa of the first material 10 on which it is deposited. This makes it possible to indirectly calculate the surface temperature of the first material 10 based on the calculated temperature of the deposited microparticle of the second material 12. Tn preferred embodiments, the temperature of the deposited microparticle of the second material 12 is the same as the surface temperature of the first material 10, meaning that the surface temperature of the first material 10 can be easily determined by calculating the temperature of the deposited microparticle of the second material 12.

In order to minimise the thermal effect of the deposited microparticle of the second material 12 on the first material 10, and thereby minimise the effect on the actual operating temperature of the first material 10 by minimising the total amount of heat conducted from the surface lOa of the first material 10 into the second material 12, the second material 12 desirably has a low thermal capacity. Moreover, in preferred embodiments, the deposited microparticle of the second material 12 is in the form of a microsphere (as hereinbefore defined). The use of microspheres, as opposed to microparticles having other forms (which are entirely within the scope of the present invention) has a number of distinct advantages which will be discussed later in this

specification.

The temperature-related characteristic of the deposited microparticle of the second material 12 that is measured using the method according to the invention may be an optical temperature-related characteristic that is optically measurable.

In one embodiment, the optically measurable temperature-related characteristic is TR radiation emitted from the deposited microparticle of the second material 12 and the emitted JR radiation is typically measured using JR imaging. In embodiments where JR imaging is used, the second material 12 from which the deposited microparticle is formed is preferably opaque to JR radiation and may, for example, be a carbon-based material such as carbon black. The use of such material is desirable since it has good JR radiation emission characteristics. The microparticle of the second material 12 could optionally comprise a surface layer that is transparent to JR radiation to thereby provide a microparticle having both high TR radiation emissivity and electrical insulation. The surface layer could, for example, be provided by coating the microparticle of the second material 12 with a suitable JR radiation transparent material.

As discussed above, JR imaging is a technique that is known and already used for measuring the operating temperature of semiconductor devices. However, by employing JR imaging in accordance with the present invention, the known drawbacks of current JR imaging techniques are overcome.

Firstly, it is possible to select the second material 12 so that it is susceptible to measurement using JR imaging. As indicated, JR opaque materials, such as carbon black, are well suited for this purpose. The temperature measurements obtained using the present method are thus totally independent of the first material 10 from which the semiconductor device is manufactured and are not affected by background radiation to the same extent as the typically JR transparent materials from which most semiconductor devices are manufactured.

Secondly, the use of microparticles, and especially microspheres, of the second material 12 increases the resolution that can be obtained using JR imaging whose spatial resolution is, as indicated, somewhat limited in present JR imaging techniques.

Jn the case of microspheres in particular, it will be appreciated that the area of point contact between the first and second materials 10, 12 is minimal and that it is, thus, possible to measure temperatures in very small regions of the surface 1 Oa of the first material 10. Although there is minimal contact between the surface 1 Oa and the deposited microsphere of the second material 12, the effective surface area of the niicrosphere is substantially greater than the point contact area to the extent that the wavelengths of JR radiation emitted by the microspheres are large enough to be detected using JR imaging. Jt is believed that a spatial surface temperature resolution in the order of luim or possibly less may be possible by effecting JR imaging of microspheres in accordance with embodiments of the present invention.

-10 -Whatever the form of the deposited microparticle of the second material 12 and however small the point contact area between the surface 1 Oa of the first material 10 and the deposited microparticle, the contact is sufficient to permit thermal coupling of the first and second materials 10, 12 to thereby enable heat to flow by conduction from the surface 1 Oa of the first material 10 into the deposited microparticle of the second material 12 so that the deposited microparticle of the second material 12 is elevated to the same, or at least substantially the same, temperature as the surface 1 Oa of the first material 10. In this regard, validation experiments have demonstrated that surface temperature measurements can be made with errors of less than 0.7°C by effecting JR imaging of carbon microspheres of the second material 12.

In another embodiment, the optically measurable temperature-related characteristic is the optical phonon activity of the deposited microparticle of the second material 12, which is typically measured using a suitable Raman spectroscopy technique, such as Micro-Raman spectroscopy. In embodiments where Raman spectroscopy is used to detect the optical phonon activity of the deposited microparticle of the second material 12, the second material 12 from which the deposited microparticle is formed may comprise semiconductor material. In this case, the first material 10 whose surface temperature is measured may be semiconductor material or a metal region of a semiconductor device.

In yet another embodiment, the optically measurable temperature-related characteristic is the thermal reflectance of the deposited microparticle of the second material 12. Thermal reflectance measurement is a widely known optical measurement technique. In embodiments where this technique is used, the second material 12 from which the deposited microparticle is formed is selected so that the surface of the microparticle has a high reflectance coefficient. This, in combination with the small contact (point contact) area between the microparticle and the surface lOa of the first material 10, permits high accuracy and high resolution surface temperature measurements to be made across the surface lOa of the first material 10.

it is often desirable to measure the surface temperature of a semiconductor device at a plurality of locations across the surface of the device to enable a temperature profile to be generated, or in other words to enable the surface temperature of the semiconductor device to be thermally mapped. Embodiments of the present method can, therefore, be used to measure the temperature of the surface 1 Oa of the first material 10 at a plurality of locations to thereby allow such thermal mapping.

In one embodiment, a single microparticle of the second material 12 is positioned at a first location on the surface 1 Oa of the first material 10 at which its temperature-related characteristic is measured and the surface temperature of the first material 10 thus calculated at that first location. The single microparticle is then removed from the surface 1 Oa so that it is no longer in point thermal contact with the surface 1 Oa before it is repositioned at a second location on the surface lOa at which its temperature-related characteristic is again measured and the surface temperature of the first material 10 calculated at that second location. This repositioning and temperature measurement process is repeated as many times as is necessary to obtain a desired surface temperature profile.

In another embodiment, a single microparticle of the second material 12 is deposited on the surface lOa of the first material 10 at a desired position and is displaced across the surface 1 Oa of the first material 10 by a probe or in another suitable manner in a desired direction. Tn this embodiment, the temperature-related characteristic of the deposited microparticle of the second material 12 is measured either continuously, or at discrete intervals, as the microparticle is displaced across the surface lOa of the first material 10. The use of a microsphere is particularly suited to this embodiment because it is able to roll across the surface lOa of the first material 10 with relative ease whilst maintaining point thermal contact with the surface 1 Oa.

In yet another embodiment, a plurality of individual microparticles of the second material 12 are positioned at a plurality of discrete locations on the surface lOa of the first material 10. In this embodiment, the temperature-related characteristic of each positioned microparticle can be measured in turn or, alternatively, the temperature- -12 -related characteristics of all of the positioned microparticles can be measured simultaneously. One possible drawback of this embodiment is that the greater the number of microparticles that are used, the greater the total amount of heat flow into the deposited microparticles will be. This could possibly affect the operating state of a semiconductor device formed using the first material and thus result in temperature measurements of reduced accuracy, but any such inaccuracy should be minimal.

An apparatus 14 for measuring the surface temperature of the first material 10 is illustrated in Figure 1. The apparatus 14 includes measuring means, such as an optical detector 16, for measuring a temperature-related characteristic of the deposited microparticle of the second material 12 and means, such as a processor 18, for calculating the surface temperature of the first material 10 using the temperature-related characteristic of the deposited microparticle of the second material 12 that is measured by the detector 16. The processor 18 may be provided by a microcomputer.

In embodiments where the optically measured temperature-related characteristic of the deposited microparticle of the second material 12 is the JR radiation emitted by the second material 12, the optical detector 16 comprises a suitable JR imaging arrangement. One suitable JR imaging arrangement is the Infrascope thermal microscope manufactured by Quantum Focus Instruments Corporation of California, USA. In embodiments where the optically measured temperature-related characteristic of the second material 12 is the phonon activity of the second material 12, the optical detector 16 typically comprises a Raman spectroscope.

Although not illustrated in Figure 1, the apparatus 14 may additionally comprise a probe or other suitable means for depositing one or more of the microparticles of the second material 12 on the surface lOa of the first material 10 at one or more locations.

Where a single microparticle of the second material 12 is deposited on the surface 1 Oa of the first material 10 and displaced across the surface lOa of the first material 10, the probe or other suitable means may operate to displace the deposited microparticle across the surface lOa in a desired direction.

-13 -Figure 2 illustrates temperature measurement profiles across a channel (the edges of which are denoted by the vertical lines) in the surface 1 0a of a semiconductor device comprising first material 10 in the form of semiconductor material and metal contact regions. As expected, the standard JR imaging technique significantly underestimates the surface temperature profile measured using the microparticle imaging technique according to embodiments of the present invention which, in the case of Figure 2, was obtained by measuring the JR radiation emitted from microparticles of the second material 12. Jndeed, it has been shown that the surface temperature profile illustrated in Figure 2 measured using the present microparticle imaging technique correlates very closely with a surface temperature profile obtained using Micro-Raman spectroscopy and also with known thermal models. Tt was possible using the present microparticle imaging technique to accurately measure the temperature of both semiconductor material and metal contact regions within the semiconductor device.

Although embodiments of the invention have been described in the preceding paragraphs with reference to various examples, it should be understood that various modifications may be made to those examples without departing from the scope of the present invention, as claimed.

For example, any suitable form of microparticle of the second material 12 may be deposited on the surface 1 Oa of the first material. A temperature-related characteristic of the microparticle of the second material 12 other than an optical temperature-related characteristic may be measured. Where an optical temperature-related characteristic of the second material 12 is measured, any suitable optical temperature-related characteristic, other than emitted JR radiation, phonon activity and thermal reflectance, may be measured.

A plurality of microparticles of the second material 12 could be dispersed in a carrier, such as a fluid, which could be applied to the surface lOa of the first material 10. The microparticles could, thus, easily be distributed across the surface lOa of the first material 10 upon application of the carrier containing the microparticles to the surface 1 Oa of the first material 10. A temperature-related characteristic of the individual -14 -microparticles of the second material 12 could then be measured as described above, thus enabling thermal mapping of the surface lOa of the first material 10.

As already described, instead of being located on the surface 1 Oa of the first material 10, one or more microparticles of the second material 12 could be at least partially embedded in the first material 10 to permit the temperature of an item in thermal contact with, and typically enclosed by, the first material 10 to be determined by calculating the temperature of the first material 10 in accordance with the foregoing method.

Claims

-15 -CLAIMS1. A method for measuring the temperature of a first material, the method comprising the steps of: (i) measuring a temperature-related characteristic of a microparticle of a second material in thermal contact with the first material; and (ii) calculating the temperature of the first material using the measured temperature-related characteristic of the microparticle of the second material.
2. A method according to claim 1, wherein the temperature-related characteristic measured during step (i) is an optically detectable characteristic.
3. A method according to claim 2, wherein the optically detectable temperature-related characteristic measured during step (i) is the infrared radiation emitted from the microparticle of the second material, and wherein step (i) comprises measuring the emitted infrared radiation using infrared imaging.
4. A method according to any preceding claim, wherein the second material is opaque to electromagnetic radiation in the infrared range.
5. A method according to any preceding claim, wherein the second material comprises carbon.
6. A method according to claim 2, wherein the optically detectable temperature-related characteristic measured during step (i) is the optical phonon activity of the microparticle of the second material, and wherein step (i) comprises measuring the optical phonon activity using Rarnan spectroscopy.
7. A method according to claim 6, wherein the second material comprises a semiconductor material.

-16 -
8. A method according to claim 2, wherein the optically detectable temperature-related characteristic measured during step (i) is the thermal reflectance of the microparticle of the second material.
9. A method according to any preceding claim, wherein step (ii) comprises calculating the temperature of the microparticle of the second material using the measured temperature-related characteristic of the microparticle of the second material and calculating the temperature of the first material based on the calculated temperature of the microparticle of the second material.
10. A method according to claim 9, wherein the temperature of the first material is substantially equal to the calculated temperature of the microparticle of the second material.
11. A method according to any preceding claim, wherein the microparticle is a microsphere.
12. A method according to any preceding claim, wherein the microparticle of the second material is in point thermal contact with a surface of the first material to permit measurement of the surface temperature of the first material at the point of contact.
13. A method according to claim 12, wherein the method comprises depositing a microparticle of the second material on the surface of the first material.
14. A method according to claim 12 or claim 13, wherein the method comprises displacing the microparticle of the second material across the surface of the first material and wherein step (i) comprises measuring the temperature-related characteristic of the microparticle during said displacement across the surface of the first material to enable the surface temperature across the surface of the first material to be calculated during step (ii).

-17 -
15. A method according to claim 12 or claim 13, wherein a plurality of individual microparticles of the second material are in point thermal contact with the surface of the first material at a plurality of discrete locations on the surface of the first material, the method comprising simultaneously or sequentially measuring the temperature-related characteristic of the microparticles during step (i) to enable the surface temperature at said discrete locations to be calculated during step (ii).
16. A method according to claim 15, wherein the plurality of microparticles of the second material are dispersed in a carrier.
17. A method according to claim 16, wherein the carrier is a fluid.
18. A method according to any preceding claim, wherein the first material comprises a semiconductor material.
19. A method according to claim 18, wherein the semiconductor material is silicon (Si), gallium arsenide (GaAs) or gallium nitride (GaN).
20. A method according to any preceding claim, wherein the first material comprises a metal.
21. A method according to any preceding claim, wherein the first material forms part of a semiconductor device.
22. A method according to any of claims 1 to 11, wherein the first material is in thernial contact with an item and is at the same temperature as the item, the microparticle of the second material being at least partially embedded in the first material.
23. A method according to claim 22, wherein the first material encloses the item.

-18 -
24. A method according to claim 22 or claim 23, wherein the first material comprises a plastics material.
25. A method for measuring the temperature profile across a first material comprising measuring the temperature of the first material at a plurality of locations using the method according to any preceding claim and generating a temperature profile based on the measured temperatures.
26. Apparatus for measuring the temperature of a first material, the apparatus comprising: measuring means for measuring a temperature-related characteristic of a microparticle of a second material in thermal contact with the first material; and means for calculating the temperature of the first material using the measured temperature-related characteristic of the microparticle of the second material.
27. Apparatus according to claim 26, wherein the apparatus includes an optical detector for measuring an optical temperature-related characteristic of the microparticle of the second material.
28. Apparatus according to claim 26, wherein the optical detector comprises an infrared imaging arrangement.
29. Apparatus according to claim 26, wherein the optical detector comprises a Raman spectroscope.
30. Apparatus according to any of claims 26 to 29, wherein the apparatus includes means for depositing a microparticle of the second material at one or more locations on a surface of the first material.
31. Apparatus according to claim 30, wherein the apparatus includes means for displacing the deposited microparticle of the second material across the surface of the first material, the measuring means being operable to measure the temperature-related -19 -characteristic of the microparticle during displacement across the surface of the first material by said displacing means to enable the surface temperature across the surface of the first material to be calculated by said calculating means.
32. A method for measuring the temperature of a first material substantially as hereinbefore described with reference to the accompanying drawings.
33. Apparatus for measuring the temperature of a first material substantially as hereinbefore described with reference to the accompanying drawings.