Determining layer thickness using photoelectron spectroscopy

• US 20060243904A1
• Filed: 04/29/2005
• Published: 11/02/2006
• Est. Priority Date: 04/29/2005
• Status: Active Grant

• Current Assignee: Intel Corporation, Nova Measuring Instruments Incorporated (Nova Ltd.)
• Original Assignee: Revera Incorporated (Nova Ltd.)
• Inventors: Schueler, Bruno
• Granted Patent: US 7,420,163 B2
• Time in Patent Office: Days
• US Class Current: 250/305
• CPC Class Codes: G01B 15/02 for measuring thickness
• CPC Class Codes: H01J 2237/2511 Auger spectrometers
• CPC Class Codes: H01J 2237/2522 of electrons (ESCA, XPS)
• CPC Class Codes: H01J 2237/2814 Measurement of surface topography

Abstract

According to one embodiment of the invention, photoelectron spectroscopy is used to determine the thickness of one or more layers in a single or multi-layer structure on a substrate. The thickness may be determined by measuring the intensities of two photoelectron species or other atom-specific characteristic electron species emitted by the structure when bombarded with photons. A predictive intensity function that is dependent on the thickness of a layer is determined for each photoelectron species. A ratio of two predictive intensity functions is formulated, and the ratio is iterated to determine the thickness of a layer of the structure. According to one embodiment, two photoelectron species may be measured from a single layer to determine a thickness of that layer. According to another embodiment, two photoelectron species from different layers or from a substrate may be measured to determine a thickness of a layer.

Claims

1. A method for determining a thickness of a layer using electron spectroscopy comprising:

determining a first predictive intensity function for a first electron species of the layer dependent on the thickness of the layer;

determining a second predictive intensity function for a second electron species of the layer dependent on the thickness of the layer;

determining a ratio of the first and second predictive intensity functions; and

iterating the ratio to determine the thickness of the layer.

2. The method of claim 1, wherein the first predictive intensity function and the second predictive intensity function are also dependent on an electron attenuation length (EAL) of the layer and a measured intensity of an electron species emitted by a layer having infinite thickness.

3. The method of claim 2, wherein the first predictive intensity function and the second predictive intensity function are dependent on an intensity of an electron emitted by a layer thicker than ten nanometers (nm).

4. The method of claim 3, wherein the first predictive intensity function and the second predictive intensity function are of the form:

5. The method of claim 1, wherein a first measured intensity of the first electron species and a second measured intensity of the second electron species are used to determine the thickness of the layer.

6. The method of claim 5, wherein the first measured intensity and the second measured intensity are fitted and wherein the first measured intensity and the second measured intensity are subject to background subtraction.

7. The method of claim 1, further comprising:

measuring a first intensity of the first electron species and a second intensity of the second electron species using x-ray photoelectron spectroscopy (XPS).

8. The method of claim 1, further comprising:

measuring a first intensity of the first electron species and a second intensity of the second electron species using Auger electron spectroscopy (AES).

34. The machine readable medium of claim 5, wherein the first measured intensity and the second measured intensity are fitted and wherein the first measured intensity and the second measured intensity are subject to background subtraction.

9. A method for determining a thickness of a layer in a multi-layer structure comprising:

determining a first predictive intensity function for a first characteristic electron species of the layer dependent on the thickness of the layer;

determining a second predictive intensity function for a second characteristic electron species of the multi-layer structure;

determining a ratio of the first and second predictive intensity functions; and

iterating the ratio to determine the thickness of the layer.

10. The method of claim 9, wherein the second characteristic electron species is of a substrate of the multi-layer structure.

11. The method of claim 9, wherein if the layer is beneath another layer of the multi-layer structure, determining the first predictive intensity function including an attenuation factor dependent on a thickness of the another layer.

12. The method of claim 11, wherein the another layer comprises an oxide of silicon.

13. The method of claim 12, wherein the thickness of the another layer is given by:

t_SiO2=sin(α

) ln[(I(Si0)/I(Si4+)*k+1].

14. The method of claim 11, wherein the first predictive intensity function is given by:

15. The method of claim 9, further comprising:

measuring a first intensity of the first characteristic electron species and a second intensity of the second characteristic electron species using x-ray photoelectron spectroscopy (XPS) or other electron spectroscopy.

16. The method of claim 9, wherein the second characteristic electron species is of another layer beneath the layer, and wherein the second predictive intensity function includes an attenuation factor dependent on the thickness of the layer.

17. The method of claim 10, wherein the second predictive intensity function includes an attenuation factor dependent on the thickness of the layer.

18. The method of claim 10, wherein the second predictive intensity function includes a second attenuation factor dependent on a second thickness of another layer between the substrate and the layer.

19. A method for determining a thickness of a layer in a multi-layer structure comprising:

bombarding the structure with radiation;

analyzing electrons ejected by the structure including a first electron species ejected by the layer and a second electron species ejected by the structure;

determining a first predictive intensity function for the first electron species dependent on a thickness of the layer and a second predictive intensity function for the second electron species;

formulating a ratio of the first and second predictive intensity functions; and

iterating the ratio to determine the thickness of the layer.

20. The method of claim 19, wherein bombarding the structure comprises:

bombarding the structure with x-rays using XPS;

wherein the first electron species and the second electron species are photoelectrons.

21. The method of claim 19, wherein bombarding the structure comprises:

bombarding the structure with electrons using Auger electron spectroscopy;

wherein the first electron species and the second electron species are Auger electrons.

22. The method of claim 19, wherein the multi-layer structure includes the layer over a second layer comprising a silicon oxide.

23. The method of claim 22, wherein the multi-layer structure includes a third layer over the layer.

24. The method of claim 22, further comprising:

determining a thickness of the second layer using t_SiO2=sin(α

) ln[(I(Si0)/I(Si4+)*k+1];

determining a thickness of the layer using the ratio;

wherein the first electron species is emitted by the layer and the first predictive intensity function is given by

$I<br><br>\left(X_i\right)=I_{\mathrm{infXi}}·<br><br>\left[1-{\mathrm{e<br><br>}}^{\left(\frac{-t_x}{{\mathrm{\lambda <br><br>}}_{\mathrm{Xi}<br><br>\left(X\right)}}\right)}\right];<br><br>$

wherein the second predictive intensity function is given by;

$F<br><br>\left(X\right)<br><br>I_{\mathrm{infX}}·<br><br>\left[1-{\mathrm{e<br><br>}}^{\left(\frac{-t_x}{{\mathrm{\lambda <br><br>}}_{X<br><br>\left(X\right)}}\right)}\right]·<br><br>{\mathrm{e<br><br>}}^{\frac{-t_y}{{\mathrm{\lambda <br><br>}}_{X<br><br>\left(Y\right)}}}.$

25. The method of claim 24, wherein the second electron species is emitted by a substrate of the structure.

26. The method of claim 19, wherein the first electron species and the second electron species are both emitted by the layer.

27. The method of claim 26, further comprising:

analyzing a third electron species emitted by a fourth layer beneath the layer;

determining a third predictive intensity function dependent on the thickness of the layer;

formulating a ratio including the third predictive intensity function and one of the first and second predictive intensity functions;

iterating the ratio to determine a thickness of the fourth layer.

28. The method of claim 27, wherein the third predictive intensity function is given by:

29. A machine readable medium having stored thereon executable program code which, when executed, causes a machine to perform a method for determining a thickness of a layer using electron spectroscopy, the method comprising:

determining a first predictive intensity function for a first electron species of the layer dependent on the thickness of the layer;

determining a second predictive intensity function for a second electron species of the layer dependent on the thickness of the layer;

determining a ratio of the first and second predictive intensity functions; and

iterating the ratio to determine the thickness of the layer.

30. The machine readable medium of claim 29, wherein the first predictive intensity function and the second predictive intensity function are also dependent on an electron attenuation length (EAL) of the layer and a measured intensity of an electron species emitted by a layer having infinite thickness.

31. The machine readable medium of claim 30, wherein the first predictive intensity function and the second predictive intensity function are dependent on an intensity of an electron emitted by a layer thicker than ten nanometers (nm).

32. The machine readable medium of claim 31, wherein the first predictive intensity function and the second predictive intensity function are of the form:

33. The machine readable medium of claim 29, wherein a first measured intensity of the first electron species and a second measured intensity of the second electron species are used to determine the thickness of the layer.

35. The machine readable medium of claim 29, the method further comprising:

measuring a first intensity of the first electron species and a second intensity of the second electron species using x-ray photoelectron spectroscopy (XPS).

36. The machine readable medium of claim 29, the method further comprising:

measuring a first intensity of the first electron species and a second intensity of the second electron species using Auger electron spectroscopy (AES).