GB2181839A - Material characterisation method and apparatus - Google Patents
Material characterisation method and apparatus Download PDFInfo
- Publication number
- GB2181839A GB2181839A GB08624924A GB8624924A GB2181839A GB 2181839 A GB2181839 A GB 2181839A GB 08624924 A GB08624924 A GB 08624924A GB 8624924 A GB8624924 A GB 8624924A GB 2181839 A GB2181839 A GB 2181839A
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- United Kingdom
- Prior art keywords
- pulses
- heat
- bolometer
- heater
- rise
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- 238000000034 method Methods 0.000 title claims abstract description 38
- 239000000463 material Substances 0.000 title claims abstract description 30
- 238000012512 characterization method Methods 0.000 title claims abstract description 15
- 230000005540 biological transmission Effects 0.000 claims abstract description 7
- 230000000875 corresponding effect Effects 0.000 claims description 8
- 238000012544 monitoring process Methods 0.000 claims description 5
- 230000002596 correlated effect Effects 0.000 claims description 2
- 230000005284 excitation Effects 0.000 description 18
- 230000004044 response Effects 0.000 description 3
- 229910052594 sapphire Inorganic materials 0.000 description 3
- 239000010980 sapphire Substances 0.000 description 3
- 229910000909 Lead-bismuth eutectic Inorganic materials 0.000 description 2
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 230000001419 dependent effect Effects 0.000 description 2
- 229910052709 silver Inorganic materials 0.000 description 2
- 239000004332 silver Substances 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000009795 derivation Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000009532 heart rate measurement Methods 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 229910052738 indium Inorganic materials 0.000 description 1
- APFVFJFRJDLVQX-UHFFFAOYSA-N indium atom Chemical compound [In] APFVFJFRJDLVQX-UHFFFAOYSA-N 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 239000010410 layer Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 239000002344 surface layer Substances 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
- 235000012431 wafers Nutrition 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N25/00—Investigating or analyzing materials by the use of thermal means
- G01N25/72—Investigating presence of flaws
Landscapes
- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Investigating Or Analyzing Materials Using Thermal Means (AREA)
Abstract
A material characterisation method, together with apparatus for performing the method, are described. Heat pulses are injected by a heater 3 into a quantity of material to be characterised, and the resultant temperature rise of a surface of the material, due to transmission of a heat pulse through the material, is monitored as a function of time, e.g. using a bolometer 5. Each heat pulse has a duration of less than the rise time of the corresponding peaks produced in the temperature against time characteristic. Subsurface damage within the material may thereby be detected. <IMAGE>
Description
SPECIFICATION
Material characterisation method and apparatus
This method relates to material characterisation methods and apparatus. In particular the invention relates to material characterisation methods and apparatus using heat pulses.
The use of heat pulses to study materials has been known for many years, the basic theory behind this technique being established by R.J.Von Gutfield in his article "Heat Pulse
Transmission" published in Physical Acoustics,
Volume 5, pages 233, published by Academic
Press in 1969. Hitherto in studies using this technique heat pulses of durations in the range 50 to 5000 nanoseconds and energy densities in the order of .1,us per square millimetre have been injected into a quantity of the material being studied, and the resultant temperature rise of a surface of the quantity due to the transmission of the pulses through the quantity as a function of time monitored.
This has enabled information such as the characteristics of heat transport in the material, and the presence of bulk impurities in the material to be derived.
It is an object of the present invention to provide a material characterisation method using heat pulses capable of providing additional information regarding the quantity of material being characterised, together with an apparatus for performing such a method.
According to the present invention a material characterisation method comprises: injecting heat pulses into a quantity of material to be characterised, and monitoring the resultant temperature rise of a surface of the quantity due to the transmission of the pulses through the quantity as a function of time, the duration of each heat pulse being less than the rise time of the corresponding peaks produced in the temperature against time characteristic.
The invention thus resides in the discovery by the inventors that by using heat pulses of such short duration information regarding the surface structure of the quantity may be derived.
Preferably the rise times of the peaks produced in said temperature against time characteristic are correlated to the characteristics of the quantity.
The invention also provides an apparatus for performing a material characterisation method, the apparatus comprising: means for injecting heat pulses into a quantity of material to be characterised and means for monitoring the resultant temperature rise of a surface of the quantity due to the transmission of the pulses through the quantity as a function of time, the duration of each of said heat pulses being less than the rise time of the corresponding peaks produced in said temperature against time characteristic.
One material characterisation method in accordance with the invention, together with apparatus for performing the method, will now be described by way of example only with reference to the accompanying drawings in which:
Figure 1 is a schematic circuit diagram of the apparatus;
Figure 2 is an enclarged schematic view of part of the apparatus of Figure 1;
Figure 3 is a time plot of the output from the bolometer incorporated in the apparatus of
Figures 1 and 2, with the shape of the excitation pulse producing the output inset in the figure;
Figures 4(a), (b) and (c) show the respective longitudinal phonon signals obtained from the bolometer at the excitation pulse widths and powers indicated;
Figure 4(d) shows the corresponding phonon signal obtained from a conventional material characterisation method;;
Figure 5 shows the transverse phonon signals obtained from the bolometer at the excitation pulse widths and powers indicated;
Figure 6 shows the magnitude of the bolometer response as a function of heater energy density for the longitudinal, fast transverse and slow transverse phonon signals obtained from the bolometer; and
Figure 7 shows the variation of the transverse to the longitudinal phonon signal amplitudes as a function of energy density; and Referring firstly to Figures 1 and 2, the method to be described is used for characterising a (2243) sample of sapphire 1. The apparatus for performing the method comprises a resistive metal film heater 3 and a
PbBi superconducting bolometer 5 as further described hereafter deposited on opposite faces of the sample 1. The heater is connected by a coaxial line 7 to a stepper attenuator 9 which is in turn connected to a pulse generator.The bolometer 5 is connected by a further coaxial line 13 via a matched T network 15 to a DC power supply 17, this serv ing to provide a biassing current to the bolometer. The matched T network 15 is also connected to a DC coupled wideband preamplifier 19 followed by a boxcar integrator 21 which also has an input from the pulse generator 11.
Referring now particularly to Figure 2 electrical contact to the heater 3 and bolometer 5 is made by means of four silver contact pads 23 evaporated onto the sample 1. In order to reduce the capacitance and inductance of the coaxial connections and thus minimise the problems of 'ringing' and pulse reflection, the ends of the coaxial lines 7, 13 are designed to make direct pressure contact to the silver pads 23 as indicated in the figure. The impedance of both the heater 3 and bolometer 5 are matched to that of their respective coaxial lines 7, 13.
In use of the apparatus the sample 1 is held in an indium faced copper block (not shown) providing a good thermal contact to a temperature controlled both stabilised at the PbBi superconducting transition temperature, the sample also being held in a vacuum. The pulse generator 11 is used to provide excitation pulses to the heater 3, these pulses having durations of between 2 and 0.8 nanoseconds, and rise times in the order of 100 picoseconds. The power density of the excitation pulses has a maximum of 800 Wmm-2. The heat pulses thus transmitted by the heater 3 into the sample 1 are detected by the bolometer 5, the preamplifier 19 and boxcar integrator giving an electronic ouput whose response time is in the order of 1 nanosecond.
A typical bolometer response for the 0.8 nanosecond excitation pulse with a power density of 800 Wmm-2 is shown in Figure 3, the form of the excitation pulse being shown inset in the figure. The general form of the plot is of conventional form for sapphire in that it shows a peak at around O.5,us which corresponds to the signal from the longitudinal mode phonons transmitted through the sample
1, with the peaks at around 0.8iLs and 0.9,us corresponding to slow and fast transverse mode phonons respectively. The longitudinal phonon peak is also shown in Figure 4, plot c with a corresponding peak shown in plot d of
Figure 4 measured with a conventional excitation pulse width of 50 nanoseconds but a greater excitation power density than is usual for such pulses for comparison.As can be seen the rise time of the conventional excitation pulse is itself equal to the width of the longitudinal phonon peak indicating that in conventional heat pulse methods the bolometer integrates the incident phonon pulses.
The rise time for the phonon peak resulting from the 0.8. nanosecond pulse however is much greater than the excitation pulse width and thus gives information relating to the characteristics of the sample. the inventors have found that for excitation pulse widths of less than 5 nanoseconds, the rise time of the peaks does not get less than a time which is a characteristic of the particular sample, even for excitation pulse widths as short as 0.8 nanoseconds. They have attributed this to diffusive phonon transport confined to a narrow subsurface damage region of the sample 1 adjacent to the heater 3 by virtue of the highly frequency dependent scattering that will occur within such a layer.
Thus by measuring the rise times of the phonon peaks in the temperature time plot an indication of the amount of subsurface damage adjacent to the surface of the sample adjacent to the heater may be obtained.
The inventors have found that the width of the longitudinal peak decreases from 20 to 10 nanoseconds for a corresponding decrease in excitation pulse width from 2 nanoseconds to 0.8 nanoseconds for the same value of pulse energy density as can be seen by comparing a and c in Figure 5. These line widths are much greater than the approximately 0.5 nanosecond widths which would be predicted for ballistic heat flow through the sample, and again can be explained by scattering in a damaged surface layer of the sample 1 adjacent to the heater 3. Thus measurement of the peak widths in the temperature-time plot may also be used to give an indication of the amount of subsurface damage.
The inventors have also performed a number of experiments relating to the variation of signal amplitude with the product of the excitation pulse magnitude and length. As can be seen by comparing plots a and b in Figure 4, the effect of attenuating the power of a 2 nanosecond excitation pulse from 800 Wmm -2 to 400 Wmm-2 is to reduce the rise time of the longitudinal peak from 20 nanoseconds to approximately 10 nanoseconds. It is found however that no further reduction in longitudinal rise time is obtained for lower power and thus energy levels. Turning now to
Figure 5, as can be seen from this figure the amplitude of the signal resulting from the 2.07
x 103 Wmm 2 ins excitation pulse is almcstidentical to that produced by 1.05 x 103
Wmm 2 2ns excitation pulse, but is a factor of two smaller than those due to a 2 ns pulse at the higher power density.These results are in contradistinction to conventional heat-pulse measurements in which the signal amplitudes are proportional to power density, and indicate that in a method in accordance with the invention the damaged regions of the sample 1 do not reach thermal equilibrium within each pulse. Figures 6 and 7 show the variation in peak amplitude with energy density, from where it can be seen that the signal amplitudes for the longitudinal and fast and slow phonon peaks all vary sublinearly with energy density. In particular there is a relative increase in amplitude of the longitudinal signal compared to that of the transverse signals.
This can be explained by the longitudinal phonons leaving the heater 3 acting as a pump of the transverse modes that are being produced by multiphonon processes within the defect region of the sample 1, this not occuring with long pulse durations since the damaged regions were able to reach thermal equilibrium during each pulse. Thus a comparision of the relative amplitudes of the peaks will yield further information relating to subsurface damage within the sample.
It will be appreciated that a method in accordance with the invention will find particular application in semidconductor technology, where surface damage to semiconductor wafers is becoming of increasing importance as devices become more surface dependent.
It will also be appreciated that whilst the method described herebefore by way of example relates to a method of characterising a sapphire sample, the method is equally applicable to the characterisation of other materials. In particular it will be appreciated that whilst in the particular method described by way of example three phonon peaks are seen, other materials and methods in accordance with the invention will cause two or more than three peaks to be produced.
It will also be appreciated that whilst in the method described herebefore by way of example heat pulses are injected into a first surface of the sample, and the resultant temperature rise on the opposite surface of the sample is monitored, the invention is equally applicable to methods where, for example the temperature rise is monitored on the same surface as that into which the heat pulses are injected, the heat pulses being reflected by one of the surfaces of the sample.
It will also be appreciated that whilst the method described herebefore by way of example relates particularly to the derivation of information relating to surface structural damage, other material information such as doping levels and information relating to two dimensional electron-phonon interactions may also be derived by a method in accordance with the invention.
Claims (10)
1. A material characterisation method comprising: injecting heat pulses into a quantity of material to be characterised, and monitoring the resultant temperature rise of a surface of the quantity due to the transmission of the pulses through the quantity as a function of time, the duration of each heat pulse being less than the rise time of the corresponding peaks produced in the temperature against time characteristic.
2. A method according to Claim 1 in which the heat pulses are each of a duration of less than 5 nanoseconds.
3. A method according to Claim 2 in which the heat pulses are each of a duration of less than 1 nanosecond.
4. A method according to any one of the preceding Claims in which the rise times of the peaks produced in the temperature against time characteristic are correlated to the characteristics of the quantity.
5. A material characterisation method substantially as hereinbefore described with reference to the accompanying drawings.
6. An apparatus for performing a material characterisation method comprising: means for injecting heat pulses into a quantity of material to be characterised, and monitoring the resultant temperature rise of a surface of the quantity due to the transmission of the pulses through the quantity as a function of time, the duration of each heat pulse being less than the rise time of the corresponding peaks produced in the temperature against time characteristic.
7. An apparatus according to Claim 6 in which said means for injecting comprises a resistive heater connected to a pulse generator, said heater being carried by said quantity.
8. An apparatus according to Claim 6 or 7 in which said means for monitoring comprises a bolometer carried by said surface of said quantity.
9. An apparatus according to Claim 7 or 8 in which high frequency connections to said heater or bolometer make direct pressure contact to electrical connections to said heater or bolometer also carried on said quantity.
10. An apparatus for performing a material characterisation method substantially as hereinbefore described with reference to the accompanying drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB858525793A GB8525793D0 (en) | 1985-10-18 | 1985-10-18 | Material characterisation method |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB8624924D0 GB8624924D0 (en) | 1986-11-19 |
| GB2181839A true GB2181839A (en) | 1987-04-29 |
| GB2181839B GB2181839B (en) | 1989-10-25 |
Family
ID=10586915
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB858525793A Pending GB8525793D0 (en) | 1985-10-18 | 1985-10-18 | Material characterisation method |
| GB8624924A Expired GB2181839B (en) | 1985-10-18 | 1986-10-17 | Material characterisation method and apparatus |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB858525793A Pending GB8525793D0 (en) | 1985-10-18 | 1985-10-18 | Material characterisation method |
Country Status (1)
| Country | Link |
|---|---|
| GB (2) | GB8525793D0 (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1999044011A1 (en) * | 1998-02-28 | 1999-09-02 | Ramseier Rubigen Ag | Infrared measuring device for measuring the thickness of a layer |
| DE19907804C1 (en) * | 1999-02-24 | 2000-03-09 | Phototherm Dr Petry Gmbh | Thermosensitive and optosensitive measuring device, e.g. to check banknotes; uses integral transformation of induced heat radiation measuring signal |
| RU2161793C2 (en) * | 1999-02-22 | 2001-01-10 | Самарская государственная архитектурно-строительная академия | Method for determination of fire resistance of flexible reinforced-concrete building constructions |
-
1985
- 1985-10-18 GB GB858525793A patent/GB8525793D0/en active Pending
-
1986
- 1986-10-17 GB GB8624924A patent/GB2181839B/en not_active Expired
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1999044011A1 (en) * | 1998-02-28 | 1999-09-02 | Ramseier Rubigen Ag | Infrared measuring device for measuring the thickness of a layer |
| RU2161793C2 (en) * | 1999-02-22 | 2001-01-10 | Самарская государственная архитектурно-строительная академия | Method for determination of fire resistance of flexible reinforced-concrete building constructions |
| DE19907804C1 (en) * | 1999-02-24 | 2000-03-09 | Phototherm Dr Petry Gmbh | Thermosensitive and optosensitive measuring device, e.g. to check banknotes; uses integral transformation of induced heat radiation measuring signal |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2181839B (en) | 1989-10-25 |
| GB8624924D0 (en) | 1986-11-19 |
| GB8525793D0 (en) | 1985-11-20 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |