Method and apparatus for measurements of patterned structures

• US 6,476,920 B1
• Filed: 06/26/2000
• Issued: 11/05/2002
• Est. Priority Date: 03/18/1998
• Status: Expired due to Term

• Current Assignee: Nova Measuring Instruments Limited (Honeywell International Inc.)
• Original Assignee: Nova Measuring Instruments Limited (Honeywell International Inc.)
• Inventors: Machavariani, Vladimir, Scheiner, David
• Primary Examiner(s): Font, Frank G.
• Assistant Examiner(s): Punnoose, Roy M.
• Application Number:
  US09/605,664
• Time in Patent Office: 862 Days
• Field of Search: 356/381, 356/372, 356/357, 356/237.5, 356/382, 356/384, 356/630, 356/632, 356/635, 356/639, 356/625, 250/372, 250/341
• US Class Current: 356/630
• CPC Class Codes: G01B 11/02 for measuring length, width or thickness G01B11/08 takes precedence
• CPC Class Codes: G01B 11/0625 with measurement of absorption or reflection
• CPC Class Codes: G01J 3/42 Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry beam switching arrangements G01J3/08
• CPC Class Codes: H01L 22/12 for structural parameters, e.g. thickness, line width, refractive index, temperature, warp, bond strength, defects, optical inspection, electrical measurement of structural dimensions, metallurgic measurement of diffusions electrical measurement of diffusions H01L22/14

Abstract

A method for measuring at least one desired parameter of a patterned structure having a plurality of features defined by a certain process of its manufacturing. The structure represents a grid having at least one cycle formed of at least two locally adjacent elements having different optical properties in respect of incident radiation. An optical model is provided, which is based on at least some of the features of the structure defined by a certain process of its manufacturing, and on the relation between a range of the wavelengths of incident radiation to be used for measurements and a pitch of the structure under measurements. The model is capable of determining theoretical data representative of photometric intensities of light components of different wavelengths specularly reflected from the structure and of calculating said at least one desired parameter of the structure. A measurement area, which is a grid cycles containing area and is substantially larger than a surface area of the structure defined by one grid cycle, is located and spectrophotometric measurements are applied to the measurement area, by illuminating it with incident radiation of a preset substantially wide wavelength range. A light component substantially specularly reflected from the measurement area is detected, and measured data representative of photometric intensities of each wavelength within the wavelength range is obtained. The measured and theoretical data are analyzed and the optical model is optimized until the theoretical data satisfies a predetermined condition. Upon detecting that the predetermined condition is satisfied, said at least one parameter of the structure is calculated.

Claims

1. A method for measuring at least one desired parameter of a patterned structure which represents a grid having at least one cycle formed of at least two locally adjacent elements having different optical properties in respect of incident radiation, the structure having a plurality of features defined by a certain process of its manufacturing, the method comprising the steps of:

a) providing an optical model, which is based on at least some of said features of the structure and on relation between wavelength range of the incident radiation to be used for measurements and pitch of the structure under measurements, and is capable of determining theoretical data representative of photometric intensities of light components of different wavelengths specularly reflected from the structure and of calculating said at least one desired parameter of the structure;

b) locating a measurement area for applying thereto spectrophotometric measurements, wherein said measurement area is a grid cycles containing area and is substantially larger than a surface area of the structure defined by one grid cycle;

c) applying the spectrophotometric measurements to said measurement area by illuminating it with incident radiation of a preset substantially wide wavelength range, detecting light component substantially specularly reflected from the measurement area, and obtaining measured data representative of photometric intensities of each wavelength within said wavelength range;

d) analyzing the measured data and the theoretical data and optimizing said optical model until said theoretical data satisfies a predetermined condition; and

e) upon detecting that the predetermined condition is satisfied, calculating said at least one parameter of the structure.

2. The method according to claim 1, wherein said at least some features of the structure on which the optical model is based are available prior to measurements.

3. The method according to claim 1, wherein said at least some features of the structure on which the optical model is based comprises nominal values of said desired parameters to be measured.

4. The method according to claim 1, wherein said at least some features of the structure on which the optical model is based comprises materials forming each of said at least two elements.

5. The method according to claim 1, wherein the step of providing the optical model comprises the step of:

estimating known optical effects, that may be produced in the structure in response to the incident radiation, and contribution of said optical effects into the detected light component.

6. The method according to claim 1, wherein said analyzing comprises the step of:

comparing the theoretical data with the measured data and providing data indicative of the relationship between the measured and theoretical data.

7. The method according to claim 1, wherein said optimizing comprises the steps of:

adjusting certain variable factors of the optical model until the theoretical data satisfies the predetermined condition and obtaining correct values of the optical model factors.

8. The method according to claim 7, wherein said certain variable factors of the optical model define contributions of known optical effects into the detected light component.

9. The method according to claim 1, wherein said predetermined condition represents a merit function defining a certain value of a goodness of fit between the measured and theoretical data.

10. The method according to claim 1, wherein said optimizing comprises the step of:

varying a value of said at least one desired parameter until the theoretical data satisfies the predetermine condition.

11. The method according to claim 1, wherein the measurement area is a part of the structure to be measured.

12. The method according to claim 1, wherein the measurement area is located on a test site representing a test pattern similar to that of the structure, the test pattern having the same design rules and layer stacks.

13. The method according to claim 1, wherein said structure is composed of n locally adjacent elements with j layers, and said photometric intensities obtained with the theoretical data are functions of effective permittivity ε

of the structure.

14. The method according to claim 13, wherein said theoretical data is determined according to the following equation:

15. The method according to claim 14, wherein the effective permittivity is described by the following tensor:

$\mathrm{\varepsilon <br><br>}=\left(\begin{array}{cc}{\mathrm{\varepsilon <br><br>}}_x& 0\\ 0& {\mathrm{\varepsilon <br><br>}}_y\end{array}\right)$

wherein tensor components ε

_X(j) and ε

_Y(j) correspond to electric field vector parallel to the X-axis and Y-axis, respectively, and are as follows;

${\left[{\mathrm{\varepsilon <br><br>}}_X<br><br>\left(j\right)\right]}^{-1}=\underset{n=1}{\overset{N}{\sum <br><br>}}<br><br>{\left[{\mathrm{\varepsilon <br><br>}}_n<br><br>\left(j\right)\right]}^{-1}<br><br>\frac{\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>X_n}{{\mathrm{\Lambda <br><br>}}_X}$${\mathrm{\varepsilon <br><br>}}_Y<br><br>\left(j\right)=\underset{n=1}{\overset{N}{\sum <br><br>}}<br><br>{\mathrm{\varepsilon <br><br>}}_n<br><br>\left(j\right)<br><br>\frac{\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>X_n}{{\mathrm{\Lambda <br><br>}}_X}$

wherein ε

_n(j) is the permittivity of j-th layer in n-th stack;

Δ

X_n is the width of the n-th stack;

N is the number of stacks.

16. The method according to claim 15, wherein said reflectivity amplitudes are determined by recurrent utilizing said tensor components.

17. The method according to claim 13, wherein the effective permittivity is described by the following tensor:

$\mathrm{\varepsilon <br><br>}<br><br>\left(j,n\right)=\left(\begin{array}{cc}{\mathrm{\varepsilon <br><br>}}_X<br><br>\left(j,n\right)& 0\\ 0& {\mathrm{\varepsilon <br><br>}}_Y<br><br>\left(j,n\right)\end{array}\right)$

wherein tensor components ε

_X(j, n) and ε

_Y(j, n) are as follows;

18. The method according to claim 17, wherein said theoretical data is determined according to the following equation:

$R_{\mathrm{TOT}}=\mathrm{\psi <br><br>}<br><br>{<br><br>\underset{n=1}{\overset{N}{\sum <br><br>}}<br><br>R_X<br><br>\left(0,n\right)<br><br>\frac{\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>X_n}{{\mathrm{\Lambda <br><br>}}_X}<br><br>}^2+\left(1-\mathrm{\psi <br><br>}\right)<br><br>{<br><br>\underset{n=1}{\overset{N}{\sum <br><br>}}<br><br>R_Y<br><br>\left(0,n\right)<br><br>\frac{\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>X_n}{{\mathrm{\Lambda <br><br>}}_X}<br><br>}^2$

wherein ψ

describes the polarization of light;

ψ

=0 for light polarized along the Y-axis, ψ

=1 for light polarized along the X-axis, ψ

=0.5 for unpolarized light;

N is the number of stacks;

R_X(0,n) and R_Y(0,n) are the reflectivity amplitudes for entire n-th stack.

19. The method according to claim 18, wherein said reflectivity amplitudes are determined by recurrent equations utilizing said tensor components.

20. The method according to claim 13, wherein said at least one cycle is two-dimensional formed by said n different locally adjacent elements aligned along X-axis, and m different locally adjacent elements aligned along Y-axis.

21. The method according to claim 20, wherein said theoretical data being determined by the following equation:

$R_{\mathrm{TOT}}=\mathrm{\psi <br><br>}<br><br>{<br><br>\underset{n=1}{\overset{N}{\sum <br><br>}}<br><br>\underset{m=1}{\overset{M}{\sum <br><br>}}<br><br>R_X<br><br>\left(0,n,m\right)<br><br>\frac{\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>X_n<br><br>\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>Y_m}{{\mathrm{\Lambda <br><br>}}_X<br><br>{\mathrm{\Lambda <br><br>}}_Y}<br><br>}^2+\left(1-\mathrm{\psi <br><br>}\right)<br><br>{<br><br>\underset{n=1}{\overset{N}{\sum <br><br>}}<br><br>\underset{m=1}{\overset{M}{\sum <br><br>}}<br><br>R_Y<br><br>\left(0,n,m\right)<br><br>\frac{\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>X_n<br><br>\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>Y_m}{{\mathrm{\Lambda <br><br>}}_X<br><br>{\mathrm{\Lambda <br><br>}}_Y}<br><br>}^2$

wherein ψ

describes the polarization of light, the condition ψ

=0 corresponding to light polarized along the Y-axis, the condition ψ

=1 corresponding to light polarized along the X-axis, the condition ψ

=0.5 corresponding to unpolarized light;

R_X(0,n,m) and R_Y(0,n,m) are reflectivity amplitudes from all different two-dimensional elements of the structure.

22. The method according to claim 21, wherein said reflectivity amplitudes are determines by recurrent equations utilizing components of the effective permittivity tensor ε

_X(j,n,m) and ε

_Y(j,n,m), which are as follows;

23. The method according to claim 1, wherein said at least one desired parameter to be measured is a width of at least one of said at least two locally adjacent elements in the grid cycle.

24. The method according to claim 1, wherein said at least one desired parameter to be measured is a depth of at least one layer of said at least one stack.

25. The method according to claim 1, wherein said at least one desired parameter to be measured is a depth of a metal-loss portion resulting from a chemical mechanical polishing applied to said structure.

26. The method according to claim 1, wherein said patterned structure is a semiconductor wafer.

27. The method according to claim 1, wherein said manufacturing process of Chemical Mechanical Planarization (CMP).

28. An apparatus for measuring at least one desired parameter of a patterned structure that represents a grid having at least one grid cycle formed of at least two locally adjacent elements having different optical properties in respect of an incident radiation, the structure having a plurality of features defined by a certain process of its manufacturing, the apparatus comprising:

a spectrophotometer illuminating a measurement area by an incident radiation of a preset substantially wide wavelength range and detecting a specular reflection light component of light reflected from the measurement area for providing measured data representative of photometric intensities of detected light within said wavelength range, wherein the measurement area is substantially larger than a surface area of the structure defined by the grid cycle; and

a processor unit coupled to the spectrophotometer, the processor unit comprising a pattern recognition software and a translation means so as to be responsive to said measured data and locate measurements, the processor being operable for

applying an optical model, based on at least some of said features of the structure and on relation between wavelength range of the incident radiation to be used for measurements and pitch of the structure under measurements, for providing theoretical data representative of photometric intensities of light specularly reflected from the structure within said wavelength range and calculating said at least one desired parameter, and

comparing said measured and theoretical data and detecting whether the theoretical data satisfies a predetermined condition.

29. The apparatus according to claim 28, wherein said spectrophotometer comprises a spectrophotometric detector and a variable aperture stop located in the optical path of light reaching the detector, the diameter of the aperture stop being variable in accordance with the grid cycle of the measured structure.

30. The apparatus according to claim 28, wherein said measurement area is located within the patterned area of said structure.

31. The apparatus according to claim 28, wherein said measurement area is located within a test site located outside the patterned area of said structure.

32. The apparatus according to claim 28, wherein each of said at least two elements is a stack including layers having different optical properties.

33. The apparatus according to claim 28, wherein said at least one desired parameter to be measured is a width of at least one of said at least two locally adjacent elements in the grid cycle.

34. The apparatus according to claim 32, wherein said at least one desired parameter to be measured is a depth of at least one layer of said at least one stack.

35. The apparatus according to claim 32, wherein said at least one desired parameter to be measured is a depth of a metal-loss portion resulting from a chemical mechanical polishing applied to said structure.

36. A working station for processing wafers progressing on a production line, wherein each of said wafers is a patterned structure that represents a grid having at least one grid cycle formed of at least two locally adjacent elements having different optical properties in respect of an incident radiation, and the structure has a plurality of features defined by a certain process of its manufacturing, the working station comprising an inspection apparatus and a support frame for supporting the wafer within an inspection plane, wherein the inspection apparatus comprises:

a spectrophotometer illuminating a measurement area by an incident radiation of a preset substantially wide wavelength range and detecting a specular reflection light component of light reflected from the measurement area for providing measured data representative of photometric intensities of detected light within said wavelength range, wherein the measurement area is substantially larger than a surface area of the structure defined by the grid cycle; and

a processor unit coupled to the spectrophotometer, the processor unit comprising a pattern recognition software and a translation means so as to be responsive to said measured data and locate measurements, the processor being operable for

applying an optical model, based on at least some of said features of the structure and on relation between wavelength range of the incident radiation to be used for measurements and pitch of the structure under measurements, for providing theoretical data representative of photometric intensities of light specularly reflected from the structure within said wavelength range and calculating said at least one desired parameter, and

comparing said measured and theoretical data and detecting whether the theoretical data satisfies a predetermined condition.

37. The working station according to claim 36, wherein said production line comprises a Chemical Mechanical Planarization (CMP) tools arrangement.