Measurement of thin film porosity

• US 7,907,264 B1
• Filed: 08/18/2008
• Issued: 03/15/2011
• Est. Priority Date: 09/07/2007
• Status: Active Grant

• Current Assignee: KLA-Tencor Corporation
• Original Assignee: KLA-Tencor Corporation
• Inventors: Krishnan, Shankar
• Primary Examiner(s): Chowdhury; Tarifur
• Assistant Examiner(s): Stock, Jr.; Gordon J
• Application Number:
  US12/193,450
• Time in Patent Office: 939 Days
• Field of Search: None
• US Class Current: 356/128
• CPC Class Codes: G01N 15/08 Investigating permeability, pore-volume, or surface area of porous materials

Abstract

A method of measuring a porosity of a film, by measuring a refractive index of the film in a first environment having a first relative humidity to produce a first refractive index measurement. The refractive index of the film is measured in a second environment having a second relative humidity, where the first relative humidity is different from the second relative humidity, to produce a second refractive index measurement. Multiple gases can be used to create the first and second environments. The first refractive index measurement and the second refractive index measurement are input into a model that correlates refractive index to film porosity, to output the porosity of the film.

Claims

1. A method of measuring a porosity of a film, the method comprising the steps of:

measuring a refractive index of the film in a first environment having a first relative humidity to produce a first refractive index measurement,

measuring the refractive index of the film in a second environment having a second relative humidity, where the first relative humidity is different from the second relative humidity to produce a second refractive index measurement, and

inputting the first refractive index measurement and the second refractive index measurement into a model that correlates refractive index to film porosity, to output the porosity of the film.

2. The method of claim 1, wherein the first environment and the second environment are created using gases having a plurality of different molecular sizes.

3. The method of claim 1, wherein the first relative humidity and the second relative humidity are both controlled to predetermined values.

4. The method of claim 1, wherein a first temperature of the first environment and a second temperature of the second environment are both controlled to predetermined values.

5. The method of claim 1, wherein the film achieves equilibrium in the first environment before measuring the first refractive index.

6. The method of claim 1, wherein the film achieves equilibrium in the second environment before measuring the second refractive index.

7. The method of claim 1, wherein a plurality of measurements of the second refractive index are made, to determine a rate and a degree by which the second refractive index changes in the second environment.

8. The method of claim 1, wherein a plurality of measurements of the second refractive index are made, to determine a rate and a degree by which the second refractive index changes in the second environment, and the rate by which the second refractive index changes in the second environment is used to determine a pore size distribution of the film, and the degree by which the second refractive index changes in the second environment is used to determine a total pore volume of the film.

9. The method of claim 1, wherein the first environment is a relatively arid environment and the second environment is a relatively humid environment.

10. The method of claim 1, wherein the first environment is created with a first gas and the second environment is created with a different second gas.

11. The method of claim 1, wherein the first environment and the second environment are both created with a single gas, where the gas has a different moisture content in each environment.

12. A method of correlating porosity to refractive index, the method comprising the steps of:

preparing a film sample,

measuring the porosity of the film sample,

measuring the refractive index of the film sample in a plurality of different environments, including at least different humidity, and

establishing a correlation between the porosity of the film sample and the refractive index of the film sample in the different environments.

13. The method of claim 12, wherein the plurality of different environments additionally comprises different temperature.

14. The method of claim 12, wherein the step of measuring the porosity of the film sample is accomplished by at least one of X-ray reflectivity or positron annihilation spectroscopy.

15. The method of claim 12, wherein the step of measuring the refractive index of the film sample is accomplished by at least one of ellipsometer and reflectometer.