System and method for optically measuring a structure

• US 5,880,838 A
• Filed: 06/05/1996
• Issued: 03/09/1999
• Est. Priority Date: 06/05/1996
• Status: Expired due to Term

• Current Assignee: California Institute of Technology
• Original Assignee: California Institute of Technology
• Inventors: Marx, David, Psaltis, Demetri
• Primary Examiner(s): KIM, ROBERT H
• Application Number:
  US08/659,168
• Time in Patent Office: 1,007 Days
• Field of Search: 356/351, 356/354, 356/355, 356/237, 356/237 G, 356/238-240, 356/359, 356/360, 250/559.19, 250/559.22, 250/559.4, 250/559.42, 250/599.44
• US Class Current: 356/498
• CPC Class Codes: G01B 11/02 for measuring length, width or thickness G01B11/08 takes precedence
• CPC Class Codes: G01B 11/2441 using interferometry
• CPC Class Codes: G01B 2210/56 Measuring geometric parameters of semiconductor structures, e.g. profile, critical dimensions or trench depth
• CPC Class Codes: G01B 2290/70 Using polarization in the interferometer
• CPC Class Codes: G01B 9/02019 contacting different points on same face of object
• CPC Class Codes: G01B 9/02024 Measuring in transmission, i.e. light traverses the object
• CPC Class Codes: G01B 9/02081 simultaneous quadrature detection, e.g. by spatial phase shifting

Abstract

A system and method for measuring the dimensions of a small (e.g., microelectronic) structure. The present invention is an optical system and method that uses a polarized light beam, reflected off or transmitted through, a structure, to measure the structural parameters, such as the lateral dimensions, vertical dimensions, height, or the type of structural material. The system employs a light source to generate a light beam that is polarized and focused onto the structure to be measured. The structure is illuminated with TE and TM polarized light. The structure is dimensioned such that the TM and TE fields are affected differently by the diffraction off the structure. As a result, either the TE or TM field can be used as a reference to analyze the phase and amplitude changes in the other field. Differences between the diffracted TE and TM far fields allow a comparison of the relationship between the amplitude and phase of those fields to determine the structural parameters of a structure.

Claims

1. A method for optically measuring structure, comprising the steps of:

a. selecting at least one structure from among a plurality of structures on a substrate by focusing a beam of polarized incident light on the selected structure, the selected structure having a plurality of structural parameters, wherein the selecting step includes focusing the beam of incident light on a plurality of aperiodic asymmetric structures;

b. diffracting the beam of incident light off the structure to form a diffracted light which is a single diverging beam of light, such that an amplitude and a phase of the single diverging beam of light depends on the polarization of the incident light beam;

c. detecting the single diverging beam of light; and

d. determining an amplitude of and a phase difference between at least two polarization components of the single diverging beam of light to measure at least one unknown structural parameter of the structure.

2. A method for optically measuring structure, comprising the steps of:

a. selecting at least one structure from among a plurality of structures on a substrate by focusing a beam of polarized incident light on the selected structure, the selected structure having a plurality of structural parameters, wherein the selecting step includes focusing the beam of incident light on a single asymmetric structure;

b. diffracting the beam of incident light off the structure to form a diffracted light which is a single diverging beam of light, such that an amplitude and a phase of the single diverging beam of light depends on the polarization of the incident light beam;

c. detecting the single diverging beam of light; and

d. determining an amplitude of and a phase difference between at least two polarization components of the single diverging beam of light to measure at least one unknown structural parameter of the structure.

3. A method for optically measuring structure, comprising the steps of:

a. selecting at least one structure from among a plurality of structures on a substrate by focusing a beam of polarized incident light on the selected structure, the selected structure having a plurality of structural parameters;

b. diffracting the beam of incident light off the structure to form a diffracted light which is a single diverging beam of light, such that an amplitude and a phase of the single diverging beam of light depends on the polarization of the incident light beam;

c. detecting the single diverging beam of light; and

d. determining an amplitude of and a phase difference between at least two polarization components of the single diverging beam of light to measure at least one unknown structural parameter of the structure,

wherein the structure has a surface contour, and the measuring step, for each polarization component, includes;

a. dividing the structure into a plurality of grid points, each grid point being located on the surface contour;

b. calculating, at each grid point, an incident field vector resulting from the beam of incident light;

c. creating a matrix from the incident field vectors;

d. calculating electric and magnetic fields along the surface contour using the matrix; and

e. calculating the amplitude and phase of the diffracted polarization component using the calculated electric and magnetic fields along the surface contour.

4. A method for optically measuring structure, comprising the steps of:

a. selecting at least one structure from among a plurality of structures on a substrate by focusing a beam of polarized incident light on the selected structure, the selected structure having a plurality of structural parameters;

b. diffracting the beam of incident light off the structure to form a diffracted light which is a single diverging beam of light, such that an amplitude and a phase of the single diverging beam of light depends on the polarization of the incident light beam;

c. detecting the single diverging beam of light; and

d. determining an amplitude of and a phase difference between at least two polarization components of the single diverging beam of light to measure at least one unknown structural parameter of the structure,

wherein the structure is a three-dimensional structure in a microelectronic circuit.

5. A method for optically measuring structure, comprising the steps of:

a. selecting at least one structure from among a plurality of structures on a substrate by focusing a beam of polarized incident light on the selected structure, the selected structure having a plurality of structural parameters;

b. diffracting the beam of incident light off the structure to form a diffracted light which is a single diverging beam of light, such that an amplitude and a phase of the single diverging beam of light depends on the polarization of the incident light beam;

c. detecting the single diverging beam of light; and

d. determining an amplitude of and a phase difference between at least two polarization components of the single diverging beam of light to measure at least one unknown structural parameter of the structure;

wherein at least one of the structural parameters is substantially greater than the wavelength of the incident light.

6. A system for optically measuring a structure having a plurality of structural parameters, comprising:

a. a source for selecting at least one structure from among a plurality of structures on a substrate by focusing a beam of incident light on the selected structure, such that the beam of incident light is diffracted by the selected structure, to form a diffracted beam which is a single diverging beam of light;

b. a detector for detecting the single diverging beam of light; and

c. means for determining an amplitude of and a phase difference between at least two polarization components of the single diverging beam of light to measure at least one unknown structural parameter of the structure, wherein the beam of incident light is focused on a plurality of aperiodic asymmetric structures.

7. A system for optically measuring a structure having a plurality of structural parameters, comprising:

a. a source for selecting at least one structure from among a plurality of structures on a substrate by focusing a beam of incident light on the selected structure, such that the beam of incident light is diffracted by the selected structure, to form a diffracted beam which is a single diverging beam of light;

b. a detector for detecting the single diverging beam of light; and

c. means for determining an amplitude of and a phase difference between at least two polarization components of the single diverging beam of light to measure at least one unknown structural parameter of the structure, wherein the beam of incident light is focused on a single asymmetric structure.

8. A system for optically measuring a structure having a plurality of structural parameters, comprising:

a. a source for selecting at least one structure from among a plurality of structures on a substrate by focusing a beam of incident light on the selected structure, such that the beam of incident light is diffracted by the selected structure, to form a diffracted beam which is a single diverging beam of light;

b. a detector for detecting the single diverging beam of light; and

c. means for determining an amplitude of and a phase difference between at least two polarization components of the single diverging beam of light to measure at least one unknown structural parameter of the structure, wherein the structure has a surface contour and the means for determining the amplitude and phase include, for each polarization component, means for;

a. dividing the structure into a plurality of grid points, each grid point being located on the surface contour;

b. calculating, at each grid point, an incident field vector resulting from the beam of incident light;

c. creating a matrix from the incident field vectors;

d. calculating electric and magnetic fields along the surface contour using the matrix; and

e. calculating the amplitude and phase of the diffracted polarization component using the calculated electric and magnetic fields along the surface contour.

9. A system for optically measuring a structure having a plurality of structural parameters, comprising:

a. a source for selecting at least one structure from among a plurality of structures on a substrate by focusing a beam of incident light on the selected structure, such that the beam of incident light is diffracted by the selected structure, to form a diffracted beam which is a single diverging beam of light;

b. a detector for detecting the single diverging beam of light; and

c. means for determining an amplitude of and a phase difference between at least two polarization components of the single diverging beam of light to measure at least one unknown structural parameter of the structure, wherein the structure is a three-dimensional structure in a microelectronic circuit.

10. A system for optically measuring a structure having a plurality of structural parameters and a surface contour, the system comprising:

a. means for selecting at least one structure from among a plurality of structures on a substrate by focusing a polarized light beam on the selected structure, such that the polarized light beam is diffracted by the selected structure to form a diffracted light which is a single diverging beam of light, the polarized light beam having a wavelength;

b. means for detecting the single diverging beam of light;

c. means for determining an amplitude and a phase of at least two polarization components of the single diverging beam of light; and

d. means for comparing the amplitude and phase of the polarization components to one another to measure at least one structural parameter of the selected structure, including, for each polarization component, means for;

(1) dividing the selected structure into a plurality of grid points, each grid point being located on the surface contour of the selected structure,

(2) calculating, at each grid point, an incident field vector resulting from the light beam,

(3) creating a matrix from the incident field vectors,

(4) calculating electric and magnetic fields along the surface contour using the matrix, and

(5) calculating the amplitude and phase of the diffracted polarization component using the calculated electric and magnetic fields along the surface contour.