Apparatus for measuring thickness profile and refractive index distribution of multiple layers of thin films by means of two-dimensional refrectometry and method of measuring the same

• US 20040246493A1
• Filed: 03/10/2004
• Published: 12/09/2004
• Est. Priority Date: 09/21/2001
• Status: Active Grant

• Current Assignee: HB SOLUTION Co., Ltd.
• Original Assignee: K'Mac Co., Ltd.
• Inventors: Kim, Jin Yong, Lee, Joong Whan, Park, Ji Jong, Kim, Yeong Ryeol
• Granted Patent: US 7,286,242 B2
• Time in Patent Office: Days
• US Class Current: 356/504
• CPC Class Codes: G01B 11/0625 with measurement of absorption or reflection

Abstract

The present invention relates to a non-contact, non-destructive measuring apparatus that measures thickness profile and refractive index distribution of a single or multiple layers of thin films by means of the principle of reflectometry. According to the present invention, by employing more than one narrow band-pass optical filters and a two-dimensional array of CCD sensors, and by finding an optimal solution for the nonlinear functional relationship between the thickness of said thin film or thin films and the corresponding refractive indexes by using an iterative numerical computation method, said apparatus simultaneously measures local area-wise thickness profile and refractive index distribution among others of said a single layer or multiple layers of thin films on a substrate.

Claims

1. An apparatus for measuring thickness and refractive index of a single or multiple layers of thin films, said apparatus comprising;

a substrate carrier for supporting a substrate;

an optical unit for providing a light source and a reflected light from said substrate for said measurements;

an optical filter set for filtering said reflected light by different wavelength;

a two-dimensional array type of CCD sensors;

an image grabber for capturing images generated by said CCD sensors;

a data processing unit for computing and generating one or more measurement data of thickness, thickness profile or refractive index of thin films using said image data captured by said image grabber in groups of pixels of at least (3×

3) pixels, and by means of repeated and iterative use of a nonlinear error minimization method;

means for computing theoretical values of reflectivity or refractive index;

means for finding a minimum error between a computed and a measured reflectivity or refractive index values by iterative and repeated use of a nonlinear error minimization method;

a system controller unit containing image processing, information processing and system control functions for processing said image data.

2. The apparatus in claim 1, wherein further comprising an image recognition function and a display monitor for displaying said information on said thickness, thickness profile, refractive index, or refractive index distribution, selectively.

3. The apparatus in claim 1, wherein further comprising a function capable of measuring thickness profile and refractive index distribution of thin films over a selected wide range of measurement up to 200 μ

m×

200 μ

m on a substrate.

4. The apparatus of claim 1, wherein further comprising a drive unit for moving said substrate carrier in steps or continuously so that said measurement can be carried out over a much wider area on a substrate.

5. The apparatus of claim 1, wherein said optical unit includes a visible light source.

6. The apparatus of claim 1, wherein said optical unit includes an ultraviolet light source.

7. The apparatus of claim 1, wherein said optical unit includes an infrared light source.

8. The apparatus of claim 1, wherein said optical filter set is constructed as a narrow band-pass optical filter wheel.

9. The apparatus of claim 1, wherein said optical filter set is constructed with linear variable optical filter set.

10. The apparatus of claim 1, wherein said optical filter set is constructed with a partially circular variable optical filter set.

11. The apparatus of claim 1, wherein said optical filter set is constructed with a linear narrow band-pass optical filter.

12. The apparatus of claim 1, wherein said optical filter set is constructed with a partially circular narrow band-pass optical filter set.

13. The apparatus in claim 1, wherein said optical filter set is constructed with a tunable filter set.

14. The apparatus in claim 13, wherein said tunable filter set is constructed with a liquid crystal tunable filter set.

15. The apparatus in claim 13, wherein said tunable filter set is constructed with a acousto-optical tunable filter set.

16. The apparatus in claim 1, wherein said data processing unit includes at least one look-up table for handling iteratively and repeatedly used variables, coefficients, blocks of mathematical expressions or partitioned mathematical expressions for speeding up said computations by avoiding unnecessary repetitive computations.

17. The apparatus of claim 2, wherein said display monitor displays the information on the surface profiles of at least one thin film in two-dimensional images.

18. The apparatus of claim 2, wherein said display monitor displays the information on the surface profiles of at least one thin film in three-dimensional images.

19. The apparatus of claim 2, wherein said display monitor displays said thickness, or thickness profile, or refractive index distribution or surface profile or any combination of these, of a single or multiple layers of thin films, selectively, as two-dimensional or three-dimensional artificially colored images in order to enhance the visual effects for better and easy inspection and evaluation of the status and characteristics of thin films.

20. A method for measuring thickness and refractive index of a single or multiple layers of thin films, said method comprising the processes of:

capturing two-dimensional images by using a two-dimensional array of CCD sensors;

discriminating said lights incident into said CCD sensors by using a narrow band-pass filter set;

measuring said thickness in two-dimensions by partitioning the pixels out of said CCD sensors in groups in order to maintain stability in measured values;

measuring said refractive index distribution as a function of position of said pixels on the surface of a substrate in two-dimensions by partitioning said pixels in groups of at least (3×

3) pixels in order to maintain stability in measured values;

finding measured values for thickness profile or refractive index distribution or both by means of iterative and repetitive use of a nonlinear error minimization method by using said data on said reflected lights captured through said two-dimensional array type of CCD sensors;

displaying the results of measuring thickness or thickness profile or refractive index distribution, or any combination of these, of a single or multiple layers of thin films, by processing said intensity of the projected lights onto said CCD sensors as a function of wavelength and also optionally the surface profiles in two-dimensional or three-dimensional representations selectively on said monitor.