Differential acoustic time of flight measurement of temperature of semiconductor substrates

Patent metadata

Field	Value
Publication number	US-9846088-B2
Application number	US-201414490430-A
Country	US
Kind code	B2
Filing date	Sep 18, 2014
Priority date	Sep 18, 2013
Publication date	Dec 19, 2017
Grant date	Dec 19, 2017

Abstract

Disclosed is a method and apparatus for measuring semiconductor substrate temperature using a differential acoustic time of flight measurement technique. The measurement is based on measuring the time of flight of acoustic (ultrasonic) waves across the substrate, and calculating a substrate temperature from the measured time of flight and the known temperature dependence of the speed of sound for the substrate material. The differential acoustic time of flight method eliminates most sources of interference and error, for example due to varying coupling between an ultrasonic transducer and the substrate. To further increase the accuracy of the differential acoustic time of flight measurement, a correlation waveform processing algorithm is utilized to obtain a differential acoustic time of flight measurement from two measured ultrasonic waveforms. To facilitate signal recognition and processing, a symmetric Lamb mode may be used as mode of excitation of the substrate.

First claim

What is claimed is:

1. A method for determining the temperature of a substrate, comprising:
disposing the substrate on a substrate support;
contacting the substrate with a first ultrasonic transducer;
contacting the substrate with a second ultrasonic transducer;
exciting a Lamb wave in the substrate by energizing the first ultrasonic transducer and the second ultrasonic transducer;
measuring at the second ultrasonic transducer a first ultrasonic waveform of the Lamb wave originating at the first ultrasonic transducer and propagating along a first path from the first ultrasonic transducer to the second ultrasonic transducer;
measuring at the second ultrasonic transducer a second ultrasonic waveform of the Lamb wave originating from the first ultrasonic transducer and propagating along a second path from the first ultrasonic transducer to the second ultrasonic transducer, wherein the second path is different than the first path;
calculating a difference of times of flight of the second ultrasonic waveform and the first ultrasonic waveform, and
determining the substrate temperature from the calculated difference of times of flight and from a known temperature dependence of the speed of sound for the substrate material.

2. The method of claim 1 , wherein the Lamb wave is a symmetric Lamb wave.

3. The method of claim 1 , wherein the Lamb wave is excited by energizing the first ultrasonic transducer and the second ultrasonic transducer in pulsed mode.

4. The method of claim 1 , wherein the first path is the shortest path between the first ultrasonic transducer and the second ultrasonic transducer.

5. The method of claim 1 , wherein the second path is longer than the first path.

6. The method of claim 1 , wherein the second path comprises at least one reflection from the substrate edge.

7. The method of claim 1 , wherein the first and second ultrasonic transducers contact the substrate edge at substantially diametrally-opposed locations on the substrate.

8. The method of claim 1 , wherein the first and second ultrasonic transducers are located proximate to each other, but not touching each other, while contacting the substrate edge.

9. The method of claim 1 , wherein the calculating of the difference of times of flight comprises:
converting the first ultrasonic waveform into a first wavelet representation;
converting the second ultrasonic waveform into a second wavelet representation; and
determining the difference of times of flight from a calculated correlation of the first and second wavelet representations.

10. The method of claim 1 , wherein the substrate temperature is determined during a semiconductor processing step performed in a semiconductor processing tool.

11. A system for determining a temperature of a substrate, comprising:
a first ultrasonic transducer configured to contact the edge of the substrate;
a second ultrasonic transducer configured to contact the edge of the substrate;
a controller for controlling the first and second ultrasonic transducers, the controller being configured to:
provide power to energize the first and second ultrasonic transducers to excite a symmetric Lamb wave in the substrate;
measure ultrasonic waveforms received by at least the second ultrasonic transducer;
calculate a difference of times of flight of a first ultrasonic waveform and a second ultrasonic waveform propagating along a first path and a second path in the substrate and measured by the second ultrasonic transducer, respectively; and
calculate a substrate temperature from the calculated difference of times of flight and a known temperature dependence of the speed of sound for the substrate material.

12. The system of claim 11 , wherein the symmetric Lamb wave is excited by energizing the first ultrasonic transducer and the second ultrasonic transducer in pulsed mode.

13. The system of claim 11 , wherein the first and second ultrasonic transducers each comprise:
a transducer element, and
a buffer rod coupled to the transducer element, and configured to contact the substrate edge.

14. The system of claim 11 , wherein the first and second ultrasonic transducers contact the substrate edge at substantially diametrally-opposed locations on the substrate.

15. The system of claim 11 , wherein the first and second ultrasonic transducers are located proximate to each other, but not touching each other, while contacting the substrate edge.

16. The system of claim 11 , wherein the controller is configured to calculate the difference of times of flight by converting the first ultrasonic waveform into a first wavelet representation; converting the second ultrasonic waveform into a second wavelet representation, calculating a correlation of the first and second wavelet representations; and determining the difference of times of flight from the calculated correlation of the first and second wavelet representations.

17. The system of claim 11 , further comprising:
a first actuator for selectably bringing into contact with, or withdrawing from the substrate, the first ultrasonic transducer, and
a second actuator for selectably bringing into contact with, or withdrawing from the substrate, the second ultrasonic transducer.

18. A method for determining the temperature distribution of a substrate, comprising:
disposing the substrate on a substrate support;
contacting the substrate with a plurality of ultrasonic transducers;
measuring a plurality of substrate temperatures in a plurality of substrate zones, each temperature measurement in each substrate zone comprising:
selecting a substrate zone in which the substrate temperature is to be measured;
exciting a Lamb wave in the substrate by energizing a selected pair of ultrasonic transducers from the plurality of ultrasonic transducers;
measuring at a second ultrasonic transducer of the selected pair of ultrasonic transducers a first ultrasonic waveform of the Lamb wave originating at a first ultrasonic transducer of the selected pair of ultrasonic transducers and propagating along a first path from the first ultrasonic transducer of the selected pair of ultrasonic transducers to the second ultrasonic transducer of the selected pair of ultrasonic transducers;
measuring at the second ultrasonic transducer of the selected pair of ultrasonic transducers a second ultrasonic waveform of the Lamb wave originating from the first ultrasonic transducer of the selected pair of ultrasonic transducers and propagating along a second path from the first ultrasonic transducer of the selected pair of ultrasonic transducers to the second ultrasonic transducer of the selected pair of ultrasonic transducers, wherein the second path is different than the first path;
calculating a difference of times of flight of the second ultrasonic waveform and the first ultrasonic waveform;
determining a temperature of the selected substrate zone from the calculated difference of times of flight and from a known temperature dependence of the speed of sound for the substrate material.

19. The method of claim 18 , wherein the Lamb wave is a symmetric Lamb wave.

20. The method of claim 18 , further comprising:
selecting a functional form for the temperature distribution of the substrate, the selected functional form having a plurality of floating parameters; and
calculating the plurality floating parameters by fitting the plurality of substrate temperatures measured in the plurality of substrate zones.

Assignees

• Tokyo Electron Ltd

Inventors

• Pei Jun
• Bao Junwei
• Tuitje Holger
• Meng Ching-Ling
• Mihaylov Mihail D

Classifications

• H10P72/0602

  Temperature monitoring · CPC title

• G01K11/24 Primary

  of the velocity of propagation of sound · CPC title

• H01L21/67248

  Electricity · mapped topic