Out-of-pocket detection system using wafer rotation as an indicator

• US 20040143412A1
• Filed: 01/16/2003
• Published: 07/22/2004
• Est. Priority Date: 01/16/2003
• Status: Active Grant

• Current Assignee: ASM IP Holding B.V. (ASM International NV)
• Original Assignee: ASM America Incorporated (ASM International NV)
• Inventors: Donald, James J.
• Granted Patent: US 6,950,774 B2
• Time in Patent Office: Days
• US Class Current: 702/150
• CPC Class Codes: G01C 9/00 Measuring inclination, e.g. by clinometers, by levels

Abstract

An optical substrate placement device is disclosed employing light from the surface of a rotating substrate in order to generate a signal component which oscillates at the frequency of rotation of the substrate. The magnitude of another signal resulting from filtering the signal component at the frequency of rotation, when processed, reveals whether the substrate is misplaced or “out-of-pocket.” Preferred embodiments employ reactor heat lamps as the light source. Methods of detecting whether a substrate is misplaced are also provided.

Claims

1. A substrate placement detection system in a substrate processing tool, comprising:

a substrate holder having a substrate pocket for holding a substrate;

a light source located above the substrate;

a rotation device operatively joined to the substrate holder in order to effectuate the rotation of the substrate holder at a rotational frequency;

an optical sensor positioned to receive light reflected from the light source off a non-central portion of a surface of the substrate, the optical sensor being configured to generate a signal; and

a processor configured to extract a component of the signal oscillating at the rotational frequency in order to determine whether the substrate is misplaced.

2. The detection system according to claim 1, wherein the substrate is a silicon wafer.

3. The detection system according to claim 1, further including an analog-to-digital converter through which the optical sensor signal is routed before being fed to the processor.

4. The detection system according to claim 1, wherein the light source is a process chamber heat lamp.

5. The detection system according to claim 1, wherein the light source includes a supplemental light source.

6. The detection system according to claim 1, wherein the processor is a computer.

7. The detection system according to claim 6, wherein the computer is configured to contain a band pass filter tuned to the rotational frequency in order to extract the component signal, the computer being further configured to apply a thresholding algorithm to the component signal to determine whether the wafer is misplaced.

8. The detection system according to claim 7, further comprising:

an absolute value determining algorithm configured to be applied to the component signal subsequent to the application of the band pass filter; and

a low pass filter being configured to be applied to the component signal resulting from the application of the absolute value determining algorithm, the low pass filter being further configured to be applied before feeding the component signal to the thresholding algorithm.

9. The detection system according to claim 8, further comprising an adaptive algorithm configured to determine a threshold for the thresholding algorithm to apply in order to reduce false misplaced substrate indications.

10. The detection system according to claim 9, wherein the adaptive algorithm is configured to reduce false misplaced substrate indications primarily due to patterns on the wafer.

11. A method of detecting substrate placement comprising:

rotating a susceptor, upon which a substrate rests, at a rotation frequency;

detecting light from a surface of the substrate;

converting the detected light to a signal;

extracting from the detected light signal a component oscillating at the rotation frequency; and

processing and interpreting the component to determine whether the substrate is misplaced.

12. The method according to claim 11, wherein the detected light comprises light from a heat lamp reflected from the substrate surface.

13. The method according to claim 11, wherein the detected light comprises light from a supplemental light source reflected from the substrate surface.

14. The method according to claim 11, wherein the detected light comprises light radiated from the substrate surface.

15. The method according to claim 11, further comprising:

routing a signal representing the detected light through an analog-to-digital converter prior to extracting the component, producing a digital signal;

extracting the component from the digital signal using a band pass filter algorithm;

applying an absolute value determining algorithm to the component signal extracted by the band pass filter algorithm to generate a magnitude of the component;

applying a thresholding algorithm to the magnitude of the component signal produced by the absolute value determining algorithm; and

determining whether the magnitude of the component indicates an out-of-pocket condition based on the application of the thresholding algorithm.

16. The method according to claim 15, further comprising producing an out-of-pocket indication signal when the thresholding algorithm indicates an out-of-pocket condition.

17. The method according to claim 16, further comprising taking corrective action when an out-of-pocket indication signal is being produced.

18. A method of detecting substrate placement, comprising:

rotating a susceptor having a substrate resting thereupon at a rotation frequency;

detecting light reflected off a surface of a substrate from a light source;

generating a signal based on the detected light reflected off the surface of the substrate;

processing the signal to extract a variation component oscillating at the rotation frequency; and

determining whether the extracted component is above a threshold.

19. The method of claim 18, further comprising generating a misplaced substrate indication when the magnitude of the extracted component exceeds the threshold.

20. The method of claim 19, further comprising applying an adaptive algorithm for determining the threshold.

21. The method of claim 20, wherein the adaptive algorithm is configured to minimize false out-of-pocket indications primarily due to patterns on the wafer.

22. The method of claim 21, wherein the adaptive algorithm is configured to minimize out-of-pocket indications primarily due to patterns on the wafer.