GB2443280A

GB2443280A - Measurement device and method

Info

Publication number: GB2443280A
Application number: GB0711749A
Authority: GB
Inventors: Iain Douglas Baikie
Original assignee: KP TECHNOLOGY Ltd
Current assignee: KP TECHNOLOGY Ltd
Priority date: 2006-06-17
Filing date: 2007-06-18
Publication date: 2008-04-30
Anticipated expiration: 2027-06-18
Also published as: GB0612071D0; GB2443280B; GB0711749D0

Abstract

A measurement device capable of measuring a contact potential difference between a first surface and a second surface separated by an insulator through the application of an external potential. The measurement device comprises a first surface having at least two sectors V1-V4 capable of collecting data independently of one another. The two or more sectors are capable of adopting different potentials with respect to the, or, each other sector. The potential of the two or more sectors are capable of independent modification with respect to the potential of the, or, each other sector. The two or more sectors are each provided with a data acquisition channel coupled to a data processing means. The measurement device may comprise a probe such as a Kelvin probe.

Description

Measurement Device and Method" The present invention relates to a

measurement device and a method for obtaining data from a measurement device.

The Kelvin probe is a non-contact, non-destructive measurement device used to investigate properties of materials. The Kelvin probe is generally used for measuring the work function difference, between a specimen and a reference material. The work function is a sensitive indicator of surface condition and is affected by adsorbed or evaporated layers, surface construction, surface charging, oxide layer imperfections and surface and bulk contamination as well as many other factors. Work function is a material property that can be defined as the minimum amount of energy that must be applied to a surface of a material in order to remove an * 15 electron from the material so that it can just exist outside the boundary of S..

the material in vacuum conditions. 5w.

A known technique for measuring work function of a surface involves bringing two conducting materials into electrical contact and quantifying * 20 the flow of charge from one material to the other. One of the conducting materials is typically a reference material having a documented value for work function and the other conducting matenal has a value of work function that is required to be measured relative to the reference.

When two conducting materials with different values of work function are electrically connected to one another, electrons in the material with the lower work function flow to the material with the higher work function. If the conducting materials are assembled to form the plates of a parallel plate capacitor, equal and opposite surface charges form on the plates.

The potential difference developed between the plates of the capacitor is t, called the contact potential and it is measured by applying an external backing potential to the capacitor until the surface charges on the plates disappear. At this point, commonly referred to as the null output, the backing potential is equal to the contact potential. The measured change is the contact potential difference (CPD). CPD can be defined as the contact potential between the reference material and the specimen surface.

The CPD measurements can be time consuming and the CPD results often require significant amplification to gain signals of the necessary strength to enable the data to be analysed. Known systems can take 2 hours to perform a high resolution scan with approximately 2500 data points for a specimen with a surface area of 1 inch x 1 inch (2.54 cm x 2.54 cm).

According to a first aspect of the present invention, there is provided a measurement device capable of measuring a contact potential difference between a first surface and a second surface separated by an insulator, * ** through the application of an external potential, the first surface having at least two sectors capable of collecting data independently of one another. *..S

The two or more sectors can be capable of adopting different potentials.

The two or more sectors can be capable of adopting different potentials with respect to the or each other sector. The potential of the two or more sectors can be capable of independent modification with respect to the potential of the or each other sector.

The two or more sectors can each be provided with a data acquisition channel coupled to a data processing means. Each data acquisition channel can be provided with an amplifier.

The data processing means can be capable of biasing the two or more sectors of the first surface with the required potential(s).

The data processing means can be mounted proximate the first surface.

The data processing means can be capable of movement with the first surface. The first surface can be provided at one end of a shaft and the data processing means can be housed within the shaft.

The data processing means can comprise a microprocessor.

The data processing means can include a measurement system capable of calculating a mean spacing of the first surface relative to the second surface using the data acquired from the two or more sectors. The measurement system can be capable of automatically signalling for or causing readjustment of the spacing between the first surface and the second surface. Thus, the spacing change can occur without substantial delay and be quasi-instantaneous. * ** * IS.

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The measurement system can be programmed with a predetermined value for the mean spacing and the measurement system can be capable of measuring an actual spacing between the first surface and the second surface and readjusting the spacing to conform to the predetermined value for mean spacing. Thus the spacing can be readjusted to conform to the predetermined spacing in real time.

The data processing means can be capable of providing an average value for work function difference between the first surface and the second surface. Contact potential difference data from at least two of the sectors can be averaged to provide an average value for work function difference.

Four sectors can be provided and two diametrically opposing sectors can be biased with a positive constant potential and two diametrically opposing sectors can be biased with a negative potential of the same value. The data processing means can be capable of averaging the contact potential difference measurements of adjacent sectors to provide values for work function that can be averaged to give an average value of the work function for the portion of the second surface corresponding and parallel to the area of the first surface.

The data processing means can be capable of amplifying the differences between the contact potential data collected by two or more of the sectors.

The sectors can be biased with a constant potential. Differences between the sectors can be amplified. The contact potential signals from adjacent sectors can be subtracted and multiplied to increase the strength of the signal and eliminate noise common to each data acquisition channel.

The measurement device can be a probe such as a Kelvin probe. The first surface can be a reference material. The first surface typically comprises a chemically and thermodynamically stable material having a known structure such as gold or stainless steel. The second surface or specimen can be any material for which the work function is required to be measured. The insulator between the first and second surfaces can be any environment that offers relatively high resistance to the passage of electric current; such as vacuum, air or other gaseous mixture. The external potential difference is typically applied by a circuit electrically connecting the first surface to the second surface.

The first surface can be at least partially transparent. The at least partially transparent surface can allow photons of incident light therethrough.

The first surface can comprise a support having a conducting material coating. The support can be substantially flat. The support can have a low surface roughness. The support can comprise glass or sapphire glass. The conducting material coating can comprise gold or indium tin oxide.

According to a further aspect of the present invention, there is provided a method for obtaining data from a measurement device including the steps of: providing a measurement device capable of measuring a contact potential difference between a first surface and a second surface separated by an insulator, through the application of an external potential; providing two or more sectors on the first surface capable of collecting data independently of one another; and obtaining data from the two or more sectors.

The method can include independently biasing each of the two or more sectors with a potential. S... * .*

The method can include amplifying a signal containing the data collected from the or each sector.

S SI

The method can include coupling each sector to a data processing means *IS via a data acquisition channel.

The method can include mounting the data processing means proximate the first surface.

The method can include providing a first surface towards the end of a shaft and housing the data processing means in said shaft.

The method can include measuring the mean spacing of the first surface relative to the second surface.

The method can include automatically adjusting the spacing between the first surface and the second surface to conform to a predetermined value.

The method can include applying a potential to two or more sectors and calculating an average value for work function difference between the first and second surfaces.

The method can include biasing the sectors with a potential, obtaining contact potential difference data from two or more of the sectors and amplifying the differences between the sectors.

:. The method can include performing measurements at different mean spacings of the first and second surfaces relative to one another. In this * .* way a pattern of voltages can be obtained for the three-dimensional * .* distribution of electric fields surrounding the second surface. e.' -

* * The method can include moving the second surface relative to the first surface. The first surface can remain stationary while the second surface *S * 25 is moved relative to the first surface to scan an area of the second surface.

Thus, the spatial resolution can be controlled by moving the specimen.

According to a separate aspect of the invention, there is provided a tip for a measurement device that is capable of measuring a contact potential difference between a first surface of the tip and a second surface through the application of an external potential, wherein the first and second surfaces are separated by an insulator and wherein the tip comprises a substrate, at least a portion of which has a conducting material coating.

The surface of the substrate to which the conducting material coating is applied is preferably substantially flat. The surface of the substrate can have a low surface roughness.

The tip can be at least partially transparent. The substrate can be glass or sapphire glass.

The conducting material coating can be gold or indium tin oxide (ITO).

The conducting material coating can cover at least 95% of the area of the first surface of the substrate.

According to a separate aspect of the present invention, there is provided a measurement device capable of measuring a contact potential difference * between a first surface and a second surface separated by an insulator, * through the application of an external potential, wherein the measurement **SI device comprises a data processing means coupled to and moveable with * ** the first surface.

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* The data processing means can comprise a microprocessor. * * S * S.. S..

The data processing means can include a measurement system capable of calculating a mean spacing of the first surface relative to the second surface. The data processing means can be capable of automatically causing readjustment of the spacing between the first and second surfaces. Thus the spacing change can occur without substantial delay.

The data processing means can be capable of biasing the first surface with different potentials.

According to another aspect of the invention, there is provided a method of processing data from a measurement device, comprising the steps of: providing a measurement device capable of measuring a contact potential difference between a first surface and a second surface separated by an insulator, through the application of an external potential, mounting a data processing means on the first surface; actuating the measurement device to acquire data; and processing at least a portion of the acquired data using the data processing means.

The method can include adjusting the potential of the first surface using the data processing means.

The method can also include measuring the mean spacing of the first surface relative to the second surface. The method can include the step of readjusting the spacing between the first surface and the second surface using the data processing means. * ** * * S * S.

Embodiments of the invention will now be described with reference to the * *, following drawings in which: Fig. 1 is a schematic diagram of a measurement device; *55 Fig. 2 is a plan view of a first surface of a measurement device having four sectors in accordance with one aspect of the present invention; Fig. 3 is a schematic view of the reference surface of Fig. 2 with outputs, X and Y; Fig. 4 is a schematic diagram of data processing options from the first surface of Fig. 3; Figs. 5(a) and 5(b) are plan and side views of a first surface and a tip respectively in accordance with another aspect of the present invention; and Figs. 6(a) and 6(b) are side views of two tips.

In the present embodiments, a first surface or reference surface is part of a measurement device in the form of a Kelvin probe.

A tip is shown generally at 10 in Fig. 1. The tip 10 comprises a tip shaft 11 having a first surface or reference surface 12 at one end thereof. The reference surface 12 is positioned adjacent and parallel to a surface 20s of a specimen 20.

The reference surface 12 is coupled to an amplifier 18 housed within the tip shaft 11. The amplifier 18 is provided to amplify signals containing contact potential data collected by the reference surface 12. The amplifier * *.* 18 is coupled to a data processing means for signal acquisition, signal * *** processing and tip potential in the form of a microprocessor unit (MPU) 14. * .S

The MPU 14 is a dedicated miniaturised microprocessor system such as a preferable interface computer (PlC) or Maxim microprocessor series and * ** functions to process data acquired at the reference surface 12. The MPU 14 is also housed within the tip shaft 11. Thus, the signal processing U..

electronics are included as part of the tip 10 and mounted within the tip shaft 11.

The MPU 14 has an output 14p to couple the MPU 14 to a tip translation voice coil or a voice coil driving unit 16. The voice coil driving unit 16 is operable to move the tip 10 relative to the specimen 20 and to vibrate the tip 10 and therefore the reference surface 12 back and forth parallel to the specimen surface 20s in a direction indicated by an arrow 22.

The MPU 14 is provided with a further output 14v to couple the MPU 14 to a computer 30. The MPU 14 has two parameters reporting to a control program provided on the computer 30: the mean spacing between the reference surface 12 and the specimen surface 20s; and relative voltage between the reference surface 12 and the specimen surface 20s. The computer 30 can process the data relating to potential supplied via an output 14v and transmit information to the MPU 14 via an input 14i.

In use, the MPU 14 receives the signal amplified by the amplifier 18 and adjusts the potential of the reference surface 12 automatically as required.

The signal is processed by the MPU 14 and the computer 30 via the output 1 4v that transmits data relating to specimen potential. Data relating to mean spacing between the reference surface 12 and the specimen surface 20s are fed to the computer 30 and the voice coil driving unit 16.

When the Kelvin probe is in operation, these measurements are taken continuously at high speed. Information regarding the relative position of the tip 10 and the specimen 20 are processed by the MPU 14 and * *0 delivered to the voice coil driving unit 16 via the output 14p. As a result, the spacing change between the reference surface 12 and the specimen * .* surface 20s is quasi-instantaneous and occurs without substantial delay. * * I SIll * **I

An advantage of the arrangement of the present invention wherein the MPU 14 is mounted on the tip 10 itself within the tip shaft 11 is that the MPU 14 receives the amplified signal from the tip 10 and can therefore adjust the tip potential automatically such that the results are effected in real time. The function of the computer 3D is to determine the mean spacing and to constantly monitor the potential of the specimen surface 20s. The overhead on the computer 30 is lower than conventional systems, because the measurement function performed by the MPU 14 monitors the mean spacing between the reference surface 12 and the specimen surface 20s. Therefore, the reference surface 12 is always close to the predetermined mean spacing at which CPD measurements are taken. This arrangement can speed up the measurement process by an order of magnitude, since on average, the previous system operated by the PC might take five attempts to arrive at each correct measurement position. The microprocessor 14 of the present invention corrects the distance between the reference surface 12 and the specimen surface 20s in real time. The quicker output from the MPU 14 allows almost instantaneous height adjustment.

In order to accommodate the data acquisition channel and/or the MPU 14 within the tip 10, the tip shaft 11 is 0.5 to 1 mm in diameter at its widest point and is designed as shown in Figs 6(a) and 6(b). The shaft 11 of the tip 10 is of sufficient dimensions to house the amplifier 18 (or an amplifier coupled to each sector as for embodiments described hereinafter) and the * S.' MPU 14. The reference surface 12 is conjoined to the shaft 11 via a S...

conical portion 13. The material of the reference surface 12 can be gold, * S. 5,..' copper, aluminium, or stainless steel.

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* .* According to one embodiment of another aspect of the present invention, * S * *S*S * Fig. 2 shows a reference surface 212 having four sectors Vi -V4 of *.S identical area arranged in a grid in a 2x2 configuration. The outer surface of the sectors Vi -V4 comprise a conducting material, typically gold or stainless steel. A separate acquisition channel (not shown) is provided for each sector Vi -V4. Each sector Vi -V4 can be biased with different potentials and the potential of each sector Vi -V4 can be modified independently of the potential of the other sectors Vi -V4. This arrangement allows the potentials of each sector Vi -V4 to be altered independently of one another and the contact potential difference data from each sector Vi -V4 can be processed in a variety of different ways.

The reference surface 212 is coupled to a Kelvin probe (not shown). The Kelvin probe is arranged such that a specimen is positioned with the specimen surface of interest at a predetermined distance from the reference surface 212 such that the reference surface 212 and specimen surface are substantially parallel to one another to thereby act as the plates of a capacitor.

Before use, the reference surface 212 and the specimen are electrically connected by an external circuit. When the external electrical contact is made between the reference surface 212 and the specimen, there is a resultant flow of electrons from the material with the lower work function to that with the higher work function. This produces a contact potential difference between the reference surface 212 and the specimen surface. * **

A backing potential can be applied by the external circuit to permit biasing S.., of one electrode with respect to the other. At the unique point where the * S. backing potential is equal to the contact potential difference, the electric field between the plates is zero resulting in a null output. At this point, the * .. work function difference between the plates is equal and opposite to the * * * S...

* potential necessary to produce a zero output signal. The work function of S. the specimen surface can be calculated by subtracting the documented value for work function of the reference surface 212 from the value obtained for work function difference. In practice, an off-null method is employed to maximise the signal to noise ratio.

The work function difference between the reference surface 212 and the specimen surface can be found by measuring the flow of charge when the reference surface 212 and the Kelvin probe are electricafly connected.

However, this produces only one measurement as the surfaces become charged and the charge must dissipate before another measurement can be made. Vibrating the Kelvin probe allows a varying capacitance to be produced. As a result of the relationship: C= Q= V d (where C is the capacitance, 0 is the charge, V is potential, is permittivity of the dielectric, A is surface area of the capacitor plates and d is the separation between the plates) as the separation d increases, the capacitance C decreases. Since the charge remains constant, the voltage must increase.

Actuation of a voice coil driving unit (not shown) within the Kelvin probe head (not shown) causes vibration of the reference surface 212 that is parallel to the specimen surface, thereby producing a varying capacitance.

The varying capacitance causes current to flow back and forth between * 20 the reference surface 212 and specimen surface acting as the plates of the capacitor. As the probe oscillates above the specimen, the voltage * change of the reference surface 212 is recorded. The backing potential is : *. the externally applied potential used to null the circuit. * ***

I I..

Experimental arrangements involving thermal processing or deposition can change the spacing between the reference surface 212 and the specimen surface. An active suspension system is employed to add or subtract an offset to the voice coil driving unit signal which effectively spaces the reference surface 212 correctly with reference to the specimen surface.

Fig. 3 shows the sectors Vi and V4 biased with a potential of +5 volts1 and the sectors V2 and V3 biased with a potential of -5 volts. The data from each sector Vi -V4 is fed to a data processing means (not shown) such as a microprocessor or a computer having four inputs. The input for each sector Vi -V4 coupled to the data processing means simultaneously transmits potential information for an area of the specimen under each sector Vi -V4. The computer software can process the information in several different ways.

The reference surface 212 can operate in a differential measurement mode. As shown by a processing method A, in Fig. 4, the contact potential signals from adjacent sectors are subtracted from one another and any differences are amplified. Accordingly, the system resolution is increased because the external noise common to both sectors is effectively cancelled out on the assumption that the level of noise is identical for each sector. Alternatively, as shown for the processing * method B, the data for from the sectors Vi and V3 and the data from the * *** sectors V2 and V4 can be added so that the differences between these values can be amplified. Using either processing method A or processing * II * S I. . * ** method B, higher gain stages can be employed by amplifying the signal prior to processing and the resolution better than 1 mV is feasible. * *I * I S S...

* The reference surface 212 allows information on the difterential voltages in the plane parallel to the specimen surface in the x and y direction as well as normal to the specimen surface in the z direction.

If the measurements are performed at different specimen to reference surface 212 spacings the resulting pattern of voltages produces a representation of the three-dimensional distribution of electric fields above the specimen.

The differential measurement mode is especially suited for use with specimens that display large work function contrasts. For example, the differential measurement mode has advantageous application in the fields of: semi-conductor wafers; solar cells; fuel cells; semi-insulators, such as polymer-electronics and organic polymers and the like. The differential measurement method is also useful for assessing surface homogeneity of a specimen. There may be a need to assess the homogeneity of the surface of certain manufactured items. Differences in signals between adjacent sectors biased with the same potential indicates differences in surface topography. The differential measurement method is also useful for interface detection since any large differences in contact potential can be amplified and thus an interface can be detected to a resolution of the spacing between adjacent sectors Vi -V4.

The technique is also useful for defect discovery. For example, the detection of fingerprints on a surface is enabled by the detection of work function inhomogenities in a surface, because the biological material * *::::* remaining on a surface has a different work function from that of the surrounding material. The technique can be usefully employed on other * .* I.' biological materials. For example, since the tissue below the skin is an ion conductor, the technique can be used on a living patient to assess wound * ** healing. * * * *S*

As an alternative, the reference surface 212 with the sectors Vi -V4 can provide conventional work function measurements. The potential information from the four sectors Vi -V4 can be averaged to give an average value for work function difference.

The sectors Vi -V4 have a smaller area than conventional reference surfaces and as a result, the sensing area of each sector Vi - V4 tends to partially overlap with an adjacent sector Vi -V4 due to the Newton fringing capacity effect. Therefore, it is possible to make a pseudo measurement of one area that includes a neighbouring area as well as an area of the specimen directly beneath the sector Vi -V4. For example, the data from Vi biased at +5 volts provides contact potential data approximately equivalent to data from a reference surface biased at +5 volts covering the area beneath the sectors Vi, V2 and V3.

Since, the potential of each sector Vi -V4 can be independently set and it is possible to achieve the conventional measurements while maintaining each sector at a constant potential but ensuring that adjacent sectors are held at different potentials thereby increasing the speed at which measurements can be taken.

The contact potential information for each sector Vi -V4 can be obtained to give the average value for work function difference between the S *IS reference surface 212 and the specimen surface. The reference surface 212 can then be translated parallel to the specimen and moved a distance * *S equal to the diameter of the reference surface 212, so that the measurement can be repeated. This method results in a much quicker *

scan since it can take 0.008 second to switch the voltage of a reference * S * surface between 5 volts and -5 volts. Therefore, holding the potential of S....DTD: adjacent sectors constant, enables conventional contact potential measurements to be obtained without the need to switch the potential and is more efficient in terms of the time required for the scan and the overhead on the computer.

Output data from each sector Vi -V4 can be directly processed into specimen voltage data and the four sectors Vi -V4 can be scanned across the sample as fast as the scanning stage will permit.

Information regarding the spacing of each sector Vi -V4 with reference to the specimen surface is averaged. Since the sectors Vi -V4 are all provided as part of the reference surface 212, they are physically connected together and thus must move as one.

The method can be repeated and measurements can be performed at different reference surface 212 to specimen surface spacings to obtain a pattern of voltages for a three-dimensional distribution of electric fields above the specimen surface.

As an alternative to increasing the speed of each scan, the reference surface 212 can be held constant and the specimen surface can be moved relative to the reference surface 212. Thus the spatial resolution can be controlled by moving the specimen. * *S *.I* * *e'.

The reference surface 212 and Kelvin probe to which it is attached can be * used to provide average contact potential difference data for many applications for example, semiconductor diagnostics and as a tool for * **investigating corrosion. This mode also provides for quality control of * technological surfaces. For example, bloanalysis of molecular layers such as DNA on a gold surface for surface reconstruction can be monitored using the technique.

A Kelvin probe having a reference surface with a number of sectors can operate in different modes at different times or in different modes at the same time. These include, differential measurement mode, conventional work function measurement mode, average work function measurement mode and mean spacing mode.

Conventional Kelvin probe tips are made from wire. There is a slight variation in the work function of each tip of the same grade of material, because each microscopic cut wire profile is different. As a result, the initial voltage levels will be different when an external contact is made between a reference surface and a specimen. The spacing of each sector of the reference surface and the specimen will also be different with a matrix tip. Due to variations in the height of the specimen surface, each sector Vi -V4 is likely to be at slightly different mean spacings.

In order to alleviate the problem of minor differences in work function between the sectors and provide sectors Vi -V4 with a more homogenous work function, a tip, shown generally in Figs. 5(a) and 5(b) at 110, is provided with a thin layer of gold is evaporated onto a substrate.

The tip 110 comprises a tip mount iii and an amplifier 113 with electrical contacts surrounding a glass plate 114. An optical adhesive 115 couples the plate 114 and a substrate 116. The substrate 116 is transparent and has a substantially flat surface having a low surface roughness. The substrate 116 can be glass or sapphire glass. The substrate 116 is provided with a thin layer of Au deposited thereon to form a reference S. surface 112. The Au can be evaporated using lithographic deposition techniques onto the substrate 116 to provide thin layers (1050 nm) of gold. S.

: The gold reference surface 112 is approximately at least 95% of the surface area of the glass substrate 116 in order to minimise glass static effects. The gold is evaporated onto the substrate 116 to produce a homogeneous surface. The reference surface 112 is as flat as the glass, which typically does not include variations in height greater than 1 micron.

However, in use the reference surface 112 may not be exactly plane parallel with respect to the specimen, so an initialisation software routine can be used to determine the spacing changes across the reference surface 112. Once the spacing change is measured at one position, the software can adjust the measured data to account for any small (0 -5 ) misalignment.

The amplifier connections coupling the amplifier 113 and the reference surface 112 are made using gold pads located on a rear face of the glass substrate 116 projecting outwardly therefrom. The reference surface 112 is an excellent electrical conductor and also allows between 50-70% of incident light therethrough. If sapphire glass is used this enables light having a wavelength of about 4 microns therethrough. Thus, the reference surface 112 is optically transparent.

In addition to the above described gold surface, tips similar to the tip 110 shown in Fig. 5(b) can be fabricated using a conducting layer of Indium-Tin oxide (ITO). ITO is a transparent conducting material, that can be deposited in thicker layers than gold. The advantages of use of ITO is that the specimen surface beneath the tip can be homogeneously illuminated by a light source located behind the tip.

A light source 117 is provided behind the tip 110 allowing tight to pass through the plate 114 and the substrate 116. The light source 117 consists of three high output, light emitting diodes (LEDs) mounted on the : probe shaft immediately behind the tip 110. This light source 117 can be used in several different ways.

A miniature colour camera (not shown) can be mounted approximately 3 cms behind the tip 110 and offset to one side by 150. The camera is mounted on the body of the voice coil actuator so that it does not vibrate, and is focussed on the specimen. Images of an area of the specimen approximately 4 times larger than the tip array can be displayed on the computer screen via an image capture program and a hardware interface.

White light LEDs can be used as an illumination source for the colour camera.

Quasi-monochromatic LEDs can be used when the specimen is a semiconductor to simultaneously provide information on semiconductor surfaces. Rapid switching of the LED5 can be used to determine the semiconductor surface photovoltage (SPy). This SPV and the semiconductor work function determined by the traditional mode of operation of the Kelvin probe, provides information on the internal band structure of the material and any defects, such as interface states.

Further, if the light source intensity is modulated, the resultant decay of charge produces information on chemical concentrations of dopant atoms within the semiconductor. This is referred to as Deep Level Transient Spectroscopy (DLTS). The light intensities from LEDs and extremely high speed switching capability make them excellent light sources for this ::* application.

Matrix tips with two or more sectors can be used with conventional systems. Alternatively, at least part of the signal processing electronics for each sector can be housed within a tip shaft as shown in Fig. 1. A greater number of sectors Vi -V4 can be provided. For example, a 4x4 tip can allow the operator to select the effective sensing area of each sector and the neighbouring sectors can effectively shield the specimen surface from

external electric fields.

Multiple tip sectors allow features to be seen that are smaller than the tip itself. The spatial resolution of the tip is dependent on the distance between the sectors. Thus, it is possible to resolve features equal to the spacing between the sectors. The distance between the sectors can be varied to determine the resolution of the tip. It is this spacing between the sectors that governs the resolution.

Modifications and improvements can be made without departing from the scope of the invention. For example, the first surface can comprise any number of sectors. e. S.

I I.

S *5

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Claims

1. A measurement device capable of measuring a contact potential difference between a first surface and a second surface separated by an insulator, through the application of an external potential, the first surface having at least two sectors capable of collecting data independently of one another.

2. A measurement device according to claim 1, wherein the two or more sectors are capable of adopting different potentials with respect to the or each other sector.

3. A measurement device according to claim 1 or claim 2, wherein the potential of the two or more sectors are capable of independent modification with respect to the potential of the or each other sector.

4. A measurement device according to any preceding claim, wherein the two or more sectors are each provided with a data acquisition channel coupled to a data processing means.

5. A measurement device according to claim 4, wherein each data acquisition channel is provided with an amplifier.

6. A measurement device according to claim 4 or claim 5, wherein the data processing means is capable of biasing the two or more sectors of :: the first surface with the required potential(s).

7. A measurement device according to any one of claims 4 to 6, wherein the data processing means is mounted proximate the first surface.

8. A measurement device according to any one of claims 4 to 7, wherein the data processing means is moveable with the first surface.

9. A measurement device according to any one of claims 4 to 8, wherein the first surface is provided at one end of a shaft and the data processing means is housed within the shaft.

10. A measurement device according to any one of claims 4 to 9, wherein the data processing means comprise a microprocessor.

11. A measurement device according to any one of claims 4 to 10, wherein the data processing means include a measurement system capable of calculating a mean spacing of the first surface relative to the second surface using the data acquired from the two or more sectors.

12. A measurement device according to claim 11, wherein the measurement system is arranged to automatically readjust the spacing between the first surface and the second surface.

13. A measurement device according to claim 11 or claim 12, wherein the measurement system can be programmed with a predetermined value for the mean spacing and the measurement system can be capable of measuring an actual spacing between the first surface and the second surface and readjusting the spacing to conform to the predetermined value for mean spacing.

14. A measurement device according to any one of claims 4 to 13, wherein the data processing means can be capable of providing an average value for work function difference between the first surface and the second surface.

15. A measurement device according to any preceding claim, wherein the contact potential difference data from at least two of the sectors is averaged to provide an average value for work function difference.

16. A measurement device according to any preceding claim, wherein sectors can be provided and two diametrically opposing sectors can be biased with a positive constant potential and two diametrically opposing sectors can be biased with a negative potential of the same value.

17. A measurement device according to any one of claims 4 to 13, wherein the data processing means are programmed to average the contact potential difference measurements of adjacent sectors to provide values for work function that are averaged to give an average value of the work function for the portion of the second surface corresponding and parallel to the area of the first surface.

18. A measurement device according to any one of claims 4 to 14, wherein the data processing means are capable of amplifying the differences between the contact potential data collected by two or more of the sectors. S. p..

19. A measurement device according to any preceding claim, wherein the sectors are biased with a constant potential.

20. A measurement device according to any preceding claim, wherein the differences between the sectors are amplified.

21. A measurement device according to any preceding claim, wherein the measurement device is a probe such as a Kelvin probe.

22. A measurement device according to any preceding claim, wherein the first surface is a reference material.

23. A measurement device according to any preceding claim, wherein the first surface comprises a chemically and thermodynamicafly stable material having a known structure

24. A measurement device according to any preceding claim, wherein the first surface is a material selected from the group consisting of: gold or stainless steel.

25. A measurement device according to any preceding claim, wherein the insulator between the first and second surfaces is selected from the group consisting of: vacuum, air and a gaseous mixture.

26. A measurement device according to any preceding claim, wherein the external potential difference is applied by a circuit electrically connecting the first surface to the second surface.

27. A measurement device according to any preceding claim, wherein S..

the first surface is at least partially transparent.

28. A measurement device according to any preceding claim, wherein the at least partially transparent surface allows photons of incident light therethrough.

29. A measurement device according to any preceding claim, wherein the first surface comprises a support having a conducting material coating.

30. A measurement device according to claim 29, wherein the support is substantially flat.

31. A measurement device according to claim 29 or claim 30, wherein the support has a low surface roughness.

32. A measurement device according to any one of claims 29 to 31, wherein the support comprises a material selected from the group consisting of: glass and sapphire glass.

33. A measurement device according to any one of claims 29 to 32, wherein the conducting material coating is selected from the group consisting of: gold and indium tin oxide.

34. A method for obtaining data from a measurement device including the steps of: providing a measurement device capable of measuring a contact potential difference between a first surface and a second surface separated by an insulator, through the application of an external potential; providing two or more sectors on the first surface capable of collecting data independently of one another; and obtaining data from the two or more sectors.

35. A method according to claim 34, including independently biasing each of the two or more sectors with a potential.

36. A method according to claim 34 or claim 35, including amplifying a signal containing the data collected from the or each sector.

37. A method according to any one of claims 34 to 36, including coupling each sector to a data processing means via a data acquisition channel.

38. A method according to claim 37, including mounting the data processing means proximate the first surface.

39. A method according to claim 37 or claim 38, including providing a first surface towards the end of a shaft and housing the data processing means in said shaft.

40. A method according to any one of claims 34 to 39, including measuring the mean spacing of the first surface relative to the second surface.

41. A method according to any one of claims 34 to 40, including automatically adjusting the spacing between the first surface and the second surface to conform to a predetermined value.

42. A method according to any one of claims 34 to 41, including applying a potential to two or more sectors and calculating an average : value for work function difference between the first and second surfaces.

43. A method according to any one of claims 34 to 42, including biasing the sectors with a potential, obtaining contact potential difference data from two or more of the sectors and amplifying the differences between s the sectors.

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44. A method according to any one of claims 34 to 43, including performing measurements at different mean spacings of the first and second surfaces relative to one another.

45. A method according to any one of claims 34 to 44, including moving the second surface relative to the first surface.

46. A method according to claim 45, including maintaining the first surface stationary while the second surface is moved relative to the first surface to scan an area of the second surface.

47. A method according to any one of claims 37 to 46, including programming the data processing means to average the contact potential difference measurements of adjacent sectors to provide values for work function that are averaged to give an average value of the work function for the portion of the second surface corresponding and parallel to the area of the first surface.

48. A method according to any one of claims 34 to 46, including amplifying the differences between the contact potential data collected by two or more of the sectors.

48. A method according to any one of claims 34 to 46, including subtracting the contact potential signals from adjacent sectors and multiplying to increase the strength of the signal and eliminate noise common to each data acquisition channel.

49. A measurement device that is capable of measuring a contact potential difference between a first surface of a tip and a second surface through the application of an external potential, wherein the first and second surfaces are separated by an insulator and wherein the tip comprises a substrate, at least a portion of which has a conducting material coating.

50. A measurement device according to claim 49, wherein a surface of the substrate to which the conducting material coating is applied is substantially flat.

51. A measurement device according to claim 49 or claim 50, wherein the tip is at least partially transparent.

52. A measurement device according to any one of claims 49 to 51, wherein the substrate is glass or sapphire glass.

53. A measurement device according to any one of claims 49 to 52.

wherein the conducting material coating is selected from the goup consisting of: gold or indium tin oxide (ITO).

54. A measurement device capable of measuring a contact potential difference between a first surface and a second surface separated by an insulator, through the application of an external potential, wherein the ::* measurement device comprises a data processing means coupled to and moveable with the first surface. S. I.

55. A measurement device according to claim 54, wherein the data processing means comprises a microprocessor.

56. A measurement device according to claim 55, wherein the data processing means can include a measurement system capable of calculating a mean spacing of the first surface relative to the second surface.

57. A method of processing data from a measurement device, comprising the steps of: providing a measurement device capable of measuring a contact potential difference between a first surface and a second surface separated by an insulator, through the application of an external potential, mounting a data processing means on the first surface; actuating the measurement device to acquire data; and processing at least a portion of the acquired data using the data processing means.

58. A method according to claim 57, including adjusting the potential of the first surface using the data processing means.

59. A method according to claim 57 or claim 58, including measuring the mean spacing of the first surface relative to the second surface and readjusting the spacing between the first surface and the second surface using the data processing means.

S *5 S. S. I.

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