Optical Inspection Apparatus and Method

• US 20080218741A1
• Filed: 10/10/2007
• Published: 09/11/2008
• Est. Priority Date: 10/17/2006
• Status: Active Grant

• Current Assignee: Kla-Tencor Technologies Corporation (KLA Corporation)
• Original Assignee: Kla-Tencor Technologies Corporation (KLA Corporation)
• Inventors: Kelly, Patrick Vincent, Murtagh, Martin Edward, Chouaib, Houssam, Guenebaut, Vincent
• Granted Patent: US 7,659,979 B2
• Time in Patent Office: Days
• US Class Current: 356/73
• CPC Class Codes: G01N 21/1717 with a modulation of one or more physical properties of the sample during the optical investigation, e.g. electro-reflectance
• CPC Class Codes: G01N 21/9501 Semiconductor wafers manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10

Abstract

In one embodiment, a modulation spectroscopy method comprises the steps of directing a probe beam and a pump beam at a sample, modulating the pump beam, and the probe beam is reflected from the sample into a detector. The sample may include a strained semiconductor. The detector may produce as output an electrical signal which comprises a large d.c. signal proportional to reflectance R of the probe beam and a small a.c. modulated signal at the modulation frequency proportional to the modulation of the reflectance ΔR of the probe beam. Both the reflectance R of the probe beam and the modulation of the reflectance ΔR of the probe beam are measured at a multiplicity of probe beam photon energies arising from different wavelengths of the probe beam, to provide a photoreflectance spectrum comprising at least one photoreflectance lineshape. The photoreflectance spectrum is analysed to measure energy differences between interband electronic transitions of the strained semiconductor, and the strain of the strained semiconductor is determined according to said energy differences.

Claims

1. A method for modulation spectroscopy inspection of a semiconductor sample, the method comprising the steps of:

directing an incident probe beam at the sample and detecting a reflected probe beam at a detector;

modulating a pump beam, and directing the modulated pump beam at the sample to cause modulation of reflectance of the probe beam so that the detector generates as output a d.c. signal proportional to reflectance R of the probe beam and an a.c. modulated signal proportional to the modulation of the reflectance Δ

R of the probe beam; and

irradiating the sample in a manner to increase the ratio Δ

R;

R

2. A method as claimed in claim 1, wherein the sample is irradiated by the generating probe beam with properties to cause the increase in the Δ

R;

R ratio.

3. A method as claimed in claim 1, wherein the sample is irradiated by a source other than the probe beam.

4. A method as claimed in claim 3, wherein the source is dedicated to achieving an increase in the Δ

R;

R ratio.

5. A method as claimed in any preceding claim, wherein the sample is irradiated prior to detection of R and Δ

R, to condition the sample.

6. A method as claimed in any preceding claim, wherein the sample is irradiated to photo-induce changes in the sample.

7. A method as claimed in claim 6, wherein the changes are transient.

8. A method as claimed in claim 6, wherein the changes are permanent.

9. A method as claimed in any preceding claim, wherein the sample is irradiated to photo-induce changes in electrical, electronic, or optical characteristics of the sample.

10. A method as claimed in any preceding claim, wherein the sample is irradiated with UV radiation.

11. A method as claimed in any of claims 1 to 9, wherein the sample is irradiated with IR radiation.

12. A method as claimed in any of claim 1 to 9, wherein the sample is irradiated with visible radiation.

13. A method as claimed in any of claims 10 to 12, wherein the sample is irradiated by a combination of UV, IR, and visible radiation.

14. A method as claimed in any preceding claim, wherein the sample is a strained semiconductor sample.