Contactless temperature measurement in a charged particle microscope

Abstract

Disclosed is a method of using a charged particle microscope for inspecting a sample mounted on a sample holder. The microscope is equipped with a solid state detector for detecting secondary particles emanating from the sample in response to irradiation of the sample with the primary beam, with the solid state detector in direct optical view of the sample. In some embodiments, the sample is mounted on a heater with a fast thermal response time. The method comprises contactless measurement of the temperature of the sample and/or sample holder using the solid state detector.

Claims

1. A method of using a charged particle microscope, the charged particle microscope equipped for inspecting a sample mounted on a sample holder with a primary beam of charged particles, the charged particle microscope equipped with a solid state detector capable of detecting secondary particles emitted from the sample in response to irradiation of the sample with the primary beam, capable of detecting photons that impinge on the solid state detector, and disposed in direct optical view of the sample, the method comprising: heating the sample and/or the sample holder with a heater having a fast thermal response time; and performing contactless measurement of the temperature of the sample and/or the sample holder, while the sample is not being irradiated by the primary beam, by detecting photons emitted from sample that impinge on the solid state detector.

2. The method of claim 1, in which the heater is a MEMS heater and the sample is disposed on the MEMS heater.

3. The method of claim 1, in which heating the sample comprises causing contactless heating of the sample and/or the sample holder using a laser, microwave heating, induction or electron beam heating.

4. The method of claim 1, wherein: the primary beam of charged particles is a primary beam of electrons or a primary beam of ions; and the solid state detector is sensitive to photons having wavelengths in the range of visible light, infrared light, or a combination thereof.

5. The method of claim 1, in which the thermal response time of the heater is less than 10 ms.

6. The method of claim 1, in which the temperature of the heater can be adjusted to exceed 1000 K.

7. The method of claim 6, wherein: heating the sample and/or the sample holder comprises heating the sample and/or the sample holder to a temperature in excess of 1000 K, and a heating rate and a cooling rate of the sample and/or the sample holder is in excess of 10.sup.4 K/s while the sample and/or the sample holder is at the temperature in excess of 1000 K.

8. The method of claim 1, further comprising detecting a change in a heating rate or a cooling rate of the sample and/or the sample holder due to a change in the heat capacity of the sample and/or the sample holder.

9. The method of claim 8, in which the change in heat capacity is caused by a phase change of the sample.

10. The method of claim 1, further comprising blanking the primary beam while performing the contactless measurement of the temperature.

11. A charged particle microscope equipped for inspecting a sample mounted on a sample holder with a primary beam of charged particles, comprising: a solid state detector capable of detecting secondary particles emitted from the sample in response to irradiation of the sample with the primary beam, capable of detecting photons that impinge on the solid state detector, disposed in direct optical view of the sample, and configured to feed a signal corresponding to radiation emissions detected by the solid state detector to a processor equipped to display an image on a display unit; and a heater controller for controlling the temperature of a heater, wherein the solid state detector is configured to: detect secondary electrons emitted from the sample while the primary beam irradiates the sample and output a first signal proportional to the intensity of the secondary electrons detected; and detect photons emitted from the sample while the primary beam does not irradiate the sample and output a second signal corresponding to the detected photons, and wherein the processor is configured to determine the temperature of the sample in response to the second signal.

12. The charged particle microscope of claim 11, in which the charged particle microscope is programmed to blank the primary beam of charged particles when determining a temperature.

13. The charged particle microscope of claim 11, capable of heating the sample to a temperature of greater than or equal to 1000 K.

14. The charged particle microscope of claim 13, in which the heater comprises a contactless heater, the contactless heater selected from the group consisting of lasers, microwave heaters, induction heaters and electron beam heaters.

15. The charged particle microscope of claim 11, equipped with a contactless heater for heating the sample and/or the sample holder, the contactless heater selected from the group consisting of lasers, microwave heaters, induction heaters and electron beam heaters.

16. The charged particle microscope of claim 11, in which the charged particle microscope is a charged particle microscope selected from the group consisting of a Transmission Electron Microscopes column, a Scanning Transmission Electron Microscope column, a Scanning Electron Microscope column, a Focused Ion Beam column, and any combination thereof.

17. The charged particle microscope of claim 11, in which the thermal response time of the solid state detector is less than 10 ms.

18. A method of measuring the temperature of a sample in a charged particle microscope using a solid state detector capable of detecting electrons and photons that impinge on the solid state detector, comprising: mounting a sample on a sample stage, the sample stage comprising a heater with a fast thermal response; irradiating the sample with a charged particle beam, detecting radiation emitted from the sample using the solid state detector while the sample is being irradiated by the charged particle beam; ceasing irradiation of the sample with the charged particle beam; detecting photons emitted from the sample after ceasing irradiation of the sample with the charged particle beam; and determining the temperature of the sample from a signal of the solid state detector generated as a result of detecting photons emitted from the sample.

19. The method of claim 18, wherein the photons emitted by the sample while the sample is not being irradiated by the charged particle beam is visible or infrared radiation.

20. The method of claim 18, further comprising determining a rate of change of the temperature of the sample.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be elucidated in more detail on the basis of exemplary embodiments and the accompanying schematic drawings, in which:

(2) FIG. 1A schematically shows a MEMS heater as seen from the bottom,

(3) FIG. 1B schematically shows a side view of the MEMS heater shown in FIG. 1A,

(4) FIG. 2 schematically shows a SSD positioned above said MEMS heater, and

(5) FIG. 3 schematically shows the signal of a SSD versus the temperature of a sample,

DETAILED DESCRIPTION OF THE DRAWINGS

(6) FIG. 1a schematically shows a MEMS heater as seen from the bottom, that is: the side removed from the side where charged particles impact on the MEMS heater.

(7) A piece of thermally resistant, electrically insulating material, such as a ceramic part 101 is covered with a metallic track 102 forming a resistive heater. To heat the track (and thus the ceramic part 101) a current is applied over pads 103A, 103B. A 4-point resistivity measurement can be made by measuring the voltage over pads 104A, 104B.

(8) The ceramic material can be a silicon comprising material, or for example a boron comprising material. Examples are SiN, SiO.sub.2, BN, or a sandwich of SiN and SiO.sub.2.

(9) Metals from the group of refractory metals (for example W, Mo, Ta, Cr, or Ti) are used as heater material for metallic track 102. The heater can be on the surface of the ceramic part, or embedded in the ceramic part (the ceramic part being for example a sandwich). Other materials from which the track may be formed are for example carbon or a semiconductive track, provided that the material is sufficiently temperature resistant and has appropriate electric properties for heating. The form of the metal track can be tuned to give an even distribution of the heat, or a spot on the ceramic with high temperature compared to its surroundings. The temperature can be measured by measuring a part of the resistance of the metal track, or by measuring the resistance of a separate, dedicated track. Such a dedicated track need not be a track of a single metal, but may be a track comprising, for example, a thermocouple.

(10) It is noted that the heated part of the ceramic part is preferably a thin film, so that little heat is conducted from this part to the microscope, where is can cause unwanted effects such as drift or damage to electronic parts such as detectors. Also the size (surface area) of the heated part should be small for said reasons.

(11) FIG. 1B schematically shows a side view of the MEMS heater shown in FIG. 1A.

(12) FIG. 1B shows the ceramic part 101 with the track 102 at one side and a sample 100 at the opposite side. Placing the sample and the heater at opposite sides avoids diffusion of sample material in the metal track or vice versa. The sample makes contact with the MEMS heater at a few points only. This will typically be the case prior to heating. After heating, the sample may wet the ceramic or it may repel the ceramic (in the latter case again contacting the ceramic at a small surface only). Heating of the sample takes place mostly through indirect heating, that is: by radiation emerging from the ceramic. Cooling takes place by radiation as well. Conduction through the relatively thin ceramic part is hardly of importance.

(13) As cooling takes place by radiation, the cooling rate is strongly dependent on the temperature: at high temperatures the cooling rate is higher than at lower temperatures.

(14) FIG. 2 schematically shows a SSD positioned above said MEMS heater

(15) FIG. 2 can be thought to be derived from FIG. 1B. Additionally to FIG. 1B a beam of particulate radiation 200 is shown, impacting on the sample 100 at location 201.

(16) From this impact location secondary radiation is emitted and detected by SSD 202 that is mounted on a pole piece 203 of a magnetic lens.

(17) The beam of particulate radiation can be a beam of electrons, for example a beam of electrons with a selectable energy of between 200 eV and 30 keV as often used in a SEM, or a beam with a selectable energy of between 40 and 300 keV, as often used in a STEM. Other energies are known to be used. The beam of particulate radiation may also be a beam of ions (positive or negative charged atoms, molecules, or clusters) with a selectable energy of, for example, between 500 eV and 40 keV, as customary used in a FIB.

(18) In all the above mentioned cases secondary radiation in the form of secondary electrons (SEs) are emitted. In the case of incoming electrons also backscattered electrons (BSEs) are formed, as well as X-rays. The SEs, BSEs and X-rays can be detected by the SSD, the SSD of a type as described in, for example, European Patent Application Publication No. EP2009705.

(19) The detector is equipped with a central hole for passing the primary beam of radiation. Said beam (and thus the impact site 201) is scanned over the surface of the sample 100.

(20) FIG. 3 schematically shows the signal of a SSD as a function of the temperature of a sample.

(21) FIG. 3 shows a signal-versus-temperature plot, in which the maximum signal is close to 255 (one byte) and the minimum signal close to zero. Other scalings can be used, for example a two-byte scaling from 0 to (2.sup.161), or a scaling from 0 to 100%. As known to the skilled person these levels can be adjusted by a first control often known as the brightness control, black level or offset and a second control often known as the gain or contrast of the processor processing the signal.

(22) The SSD is not sensitive for long wave length, and as a consequence no or very little change in signal occurs for a temperature of 800 K or less. For a temperature in excess of approximately 800 K, more specifically in excess of 1000 K, the signal of the detector is sufficiently dependent on the temperature to use it for measuring the temperature.

(23) It is noted that before use a temperature versus signal plot for the SSD signal needs to be determined. This can be a factory setting, or can be determined prior to an experiment with a sample on the heater (empty heater). The temperature of the (empty) MEMS heater itself can be a factory calibration, or a calibration using a four point measurement of Ohmic resistance, or another type of temperature dependent measurement of the metal track. The temperature dependency of the SSD can also be based on a comparison of the signal of the SSD with prior determined temperature curves. Each of these methods has its pros and cons. It is mentioned that the size of the hot area may vary with the volume of the sample, the blackness of the sample (that is: in how far is the emitted radiation black body radiation) etc., resulting in changes in temperature versus signal plots.

(24) Although FIG. 3 can be interpreted such that for temperatures above 1150 K clipping of the detector signal occurs, this is not the case: using a lower gain the detector signal can be kept below its maximum value.

CITED NON-PATENT LITERATURE

(25) [-1-] Application Note Aduro AA01.2; http://website.protochips.netdna-cdn.com/images/stories/aa01.2.pdf [-2-] High-Temperature SEM DEMO; http://www.mse.ucla.edu/events/events-archive/2013/high-temperature-sem-demo