Evaluating sidewall coverage in a semiconductor wafer

• US 20020151092A1
• Filed: 02/16/2001
• Published: 10/17/2002
• Est. Priority Date: 02/16/2001
• Status: Active Grant

• Current Assignee: Applied Materials Incorporated
• Original Assignee: Applied Materials Incorporated
• Inventors: Li, Jiping, Borden, Peter G.
• Granted Patent: US 6,911,349 B2
• Time in Patent Office: Days
• US Class Current: 438/16
• CPC Class Codes: G01N 21/55 Specular reflectivity
• CPC Class Codes: G01R 31/307 of integrated circuits

Abstract

A sidewall or other feature in a semiconductor wafer is evaluated by illuminating the wafer with at least one beam of electromagnetic radiation, and measuring intensity of a portion of the beam reflected by the wafer. Change in reflectance between measurements provides a measure of a property of the feature. The change may be either a decrease in reflectance or an increase in reflectance, depending on the embodiment. A single beam may be used if it is polarized in a direction substantially perpendicular to a longitudinal direction of the sidewall. A portion of the energy of the beam is absorbed by the sidewall, thereby to cause a decrease in reflectance when compared to reflectance by a flat region. Alternatively, two beams may be used, of which a first beam applies heat to the feature itself or to a region adjacent to the feature, and a second beam is used to measure an increase in reflectance caused by an elevation in temperature due to heat transfer through the feature. The elevation in temperature that is measured can be either of the feature itself, or of a region adjacent to the feature.

Claims

1. A method of evaluating a feature in a semiconductor wafer, the method comprising:

illuminating the wafer with a beam of electromagnetic radiation having a majority of energy polarized in a direction other than parallel to a longitudinal direction of the feature; and

measuring intensity of a portion of the beam reflected by the wafer.

2. The method of claim 1 wherein:

the feature includes a sidewall of a groove; and

the act of measuring is performed repeatedly at a plurality of locations transverse to the longitudinal direction of the groove.

3. The method of claim 2 wherein:

the beam has a wavelength greater than thickness of the sidewall.

4. The method of claim 1 wherein:

the beam has a wavelength greater than a dimension of the feature; and

the beam forms on the wafer a spot of a diameter greater than the dimension.

5. The method of claim 1 wherein:

the feature includes a trace of reflective material.

6. The method of claim 1 wherein:

the wafer includes a layer located between a source of the beam and the feature; and

the layer is at least partially transmissive, so that the portion passes through the layer.

7. The method of claim 1 wherein:

the beam has a majority of energy polarized in a direction at least substantially perpendicular to the longitudinal direction.

8. The method of claim 1 wherein:

the beam has a predetermined wavelength; and

the method further comprises filtering light of a wavelength other than the predetermined wavelength.

9. The method of claim 1 wherein the wafer has a plurality of features including the feature, and the method further comprises:

performing the act of measuring for each feature of the plurality; and

comparing measurements of multiple features.

10. The method of claim 9 wherein:

each feature is a sidewall; and

the act of comparing includes comparing measurements of two sidewalls located opposite to one another in a groove.

11. The method of claim 1 wherein the beam is a first beam, and the method further comprises:

illuminating the wafer with a second beam of electromagnetic radiation.

12. The method of claim 11 wherein:

the first beam forms a first spot on the wafer, the second beam forms a second spot;

the act of measuring includes measuring with the first spot and the second spots located on opposite sides of the feature; and

the method further comprises measuring with the first spot and the second spots located on the same side of the feature.

13. The method of claim 11 wherein:

the second spot at least partially overlaps the first spot.

14. The method of claim 13 wherein:

the first beam has a first wavelength different from a second wavelength of the second beam;

the second beam is modulated at a predetermined frequency; and

the act of measuring includes measuring intensity of the second beam having the second wavelength and modulated at the predetermined frequency.

15. The method of claim 13 wherein:

the first beam is polarized substantially perpendicular to the longitudinal direction.

17. The method of claim 16 further comprising:

determining a coefficient of a function that fits the measurements;

comparing the coefficient against a predetermined limit and performing the changing based on an outcome of the comparing.

19. The method of claim 18 wherein:

each of the two beams includes unpolarized light.

20. The method of claim 18 wherein:

each of the two beams includes light polarized in a direction other than parallel to a longitudinal direction of the feature.

21. The method of claim 18 wherein:

the method further includes modulating intensity of a first beam at a predetermined frequency, said predetermined frequency being sufficiently small to avoid creation of a wave; and

the act of performing includes measuring intensity of a portion of the second beam reflected by the wafer, the portion being modulated at the predetermined frequency.

22. The method of claim 18 further comprising:

performing a second measurement with the first spot and the second spots located on the same side of the feature.

24. The method of claim 22 wherein:

the method further includes modulating intensity of the first beam at a predetermined frequency, said predetermined frequency being sufficiently small to avoid creation of a wave; and

the act of measuring includes measuring intensity of a portion of the second beam reflected by the wafer, the portion being modulated at the predetermined frequency.

25. The method of claim 22 wherein:

each of the two beams is a laser beam.

26. The method of claim 22 wherein:

the first beam is an electron beam; and

the second beam is a laser beam.

27. The method of claim 22 wherein:

the first beam forms a first spot; and

the second beam forms a second spot that at least partially overlaps the first spot.

28. The method of claim 22 further comprising:

forming the feature by using at least one process parameter; and

changing the process parameter depending on measurements obtained from the act of measuring.

30. The apparatus of claim 29 further comprising:

a circuit coupled to the laser to move the beam along a line across the feature; and

a monitor for displaying a graph of a signal generated by the photosensitive element as a function of distance along the line.

31. The apparatus of claim 30 wherein:

the line is at least substantially perpendicular to the longitudinal direction of the feature.

32. The apparatus of claim 29 further comprising:

an oscillator capable of oscillating at a frequency lower than 25000 Hz, the oscillator being coupled to the laser source; and

a lock-in amplifier coupled to said oscillator and to said photosensitive element.

33. The apparatus of claim 32 wherein during operation:

said oscillator causes said laser source to generate said beam at an intensity modulated at said frequency; and

said lock-in amplifier generates a signal indicative of reflectivity of said wafer.

34. The apparatus of claim 29 further comprising:

a computer coupled to the photosensitive element and programmed to determine a dimension of the feature.

35. The apparatus of claim 34 further comprising:

a memory having encoded therein values generated from at least one test wafer having a feature of a known property;

wherein the computer is programmed to use a signal generated by the photosensitive element to look up a value of property for the wafer, based on the values in memory.

37. The apparatus of claim 36 further comprising:

means for displaying measurements generated by the means for measuring, as a function of distance.

16. A method of evaluating wafers during fabrication, the method comprising:

forming a feature of conductive material in a wafer by using at least one process parameter;

illuminating the wafer with a beam of electromagnetic radiation having a majority of energy polarized in a direction other than parallel to a longitudinal direction of the feature; and

repeatedly measuring intensity of a portion of the beam reflected by the wafer at a plurality of locations transverse to the longitudinal direction; and

changing the process parameter depending on measurements obtained from the act of repeatedly measuring.

18. A method of evaluating a feature in a semiconductor wafer, the method comprising:

illuminating the wafer with two beams, each beam forming a spot; and

performing a measurement with the first spot and the second spots located on opposite sides of the feature.

23. A method of evaluating a feature in a semiconductor wafer, the method comprising:

illuminating the wafer with two beams, a first beam having a first intensity larger than a second intensity of a second beam, the first beam having a majority of energy polarized in a direction other than parallel to a longitudinal direction of the feature; and

measuring intensity of a portion of the second beam reflected by the wafer

29. An apparatus for evaluating a feature in a wafer, the apparatus comprising:

a laser source for generating a beam polarized in a direction other than parallel to a longitudinal direction of the feature; and

a photosensitive element located in a path of radiation of electromagnetic energy from the wafer.

36. An apparatus comprising:

means for illuminating a semiconductor wafer with a beam of electromagnetic radiation having a majority of energy polarized in a direction other than parallel to a longitudinal direction of the feature; and

means for measuring intensity of a portion of the beam reflected by the wafer, the means for measuring being coupled to the means for illuminating.