Apparatus and method for determining the elemental compositions and relative locations of particles on the surface of a semiconductor wafer

• US 5,742,658 A
• Filed: 05/23/1996
• Issued: 04/21/1998
• Est. Priority Date: 05/23/1996
• Status: Expired due to Fees

• Current Assignee: Advanced Micro Devices, Inc.
• Original Assignee: Advanced Micro Devices, Inc.
• Inventors: Hossain, Tim Z., Tiffin, Donald A.
• Primary Examiner(s): Porta, David P.
• Application Number:
  US08/653,727
• Time in Patent Office: 698 Days
• Field of Search: 378/44, 378/45, 378/46, 378/48, 378/49, 378/50, 378/84
• US Class Current: 378/44
• CPC Class Codes: G01N 2223/076 X-ray fluorescence
• CPC Class Codes: G01N 23/20 by using diffraction of the radiation by the materials, e.g. for investigating crystal structure; by using scattering of the radiation by the materials, e.g. for investigating non-crystalline materials; by using reflection of the radiation by the materials
• CPC Class Codes: G01N 23/223 by irradiating the sample with X-rays or gamma-rays and by measuring X-ray fluorescence
• CPC Class Codes: G01R 31/2831 Testing of materials or semi-finished products, e.g. semiconductor wafers or substrates G01R31/318511 takes precedence; testing during manufacture H01L22/00
• CPC Class Codes: G01R 31/302 Contactless testing G01R31/66 takes precedence
• 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

An apparatus and method are presented for determining the elemental compositions and relative locations of particles on a surface of a semiconductor wafer. An exposed region of the surface of the semiconductor wafer is subjected to a beam of primary X-ray photons, and secondary X-ray photons emitted by atoms of elements on and just under the surface of the semiconductor wafer are detected by an X-ray detector array which includes multiple X-ray detectors. Each X-ray detector produces an output signal which is proportional to energy levels of incident X-ray photons. The X-ray detectors are laterally displaced from one another, and arranged to allow two-dimensional resolution of detected secondary X-ray photons emitted by atoms of elements on the surface of the semiconductor wafer. The X-ray detector array is preferably an electronic area image sensor including a two-dimensional array of photosensor elements formed upon a monolithic semiconductor substrate. With adequate resolution, the X-ray detector array may also provide information as to the relative sizes of particles on the surface of the semiconductor wafer. By virtue of an employed total reflection X-ray fluorescence (TXRF) technique, substantially all of the detected X-ray photons are secondary X-ray photons emitted by atoms of elements located on and just under the exposed surface of the semiconductor wafer.

Claims

1. An apparatus for determining the elemental composition and relative location of a particle located upon a surface of a semiconductor wafer, comprising:

an X-ray source configured to produce a plurality of primary X-ray photons, wherein said plurality of primary X-ray photons forms a primary X-ray beam, and said primary X-ray beam is incident upon the surface of the semiconductor wafer; and

a plurality of X-ray detectors laterally displaced in more than one direction, wherein each of said plurality of X-ray detectors is positioned to receive a secondary X-ray photon emitted by at least one atom present within said particle.

2. The apparatus as recited in claim 1, wherein said at least one atom comprises a plurality of atoms.

3. The apparatus as recited in claim 2, wherein said plurality of atoms are associated with different elements.

4. The apparatus as recited in claim 1, wherein each of said plurality of X-ray detectors is configured to produce an output signal, wherein said output signal is proportional to an energy level of said secondary X-ray photon.

5. The apparatus as recited in claim 1, wherein the primary X-ray beam is incident upon an exposed region of the surface of the semiconductor wafer, the particle is located within the exposed region, and the plurality of X-ray detectors is positioned adjacent to the exposed region.

6. The apparatus as recited in claim 1, wherein said plurality of X-ray detectors is arranged to allow two-dimensional resolution of detected secondary X-ray photons emitted by atoms of elements on the surface of the semiconductor wafer.

7. The apparatus as recited in claim 1, wherein an angle of incidence formed between the primary X-ray beam and the surface of the semiconductor wafer, measured in a plane containing the primary X-ray beam and normal to the surface of the semiconductor wafer, is less than 0.2 degree.

8. The apparatus as recited in claim 1, wherein the X-ray source comprises a rotating anode.

9. The apparatus as recited in claim 8, wherein the rotating anode comprises tungsten.

10. The apparatus as recited in claim 1, wherein said plurality of X-ray detectors comprises an electronic area image sensor including a plurality of photosensor elements arranged to form a two-dimensional array upon a monolithic semiconductor substrate.

11. An apparatus for determining the elemental composition and relative location of a particle located upon a surface of a semiconductor wafer, comprising:

an X-ray source configured to produce a beam of polychromatic primary X-ray photons;

a multilayer monochromator aligned to receive said beam of polychromatic primary X-ray photons and configured to produce a beam of monochromatic primary X-ray photons, wherein said beam of monochromatic primary X-ray photons is incident upon the surface of the semiconductor wafer;

an X-ray detector array comprising a plurality of laterally displaced X-ray detectors, wherein each of said plurality of X-ray detectors is (i) positioned to receive a secondary X-ray photon emitted by at least one atom present within said particle, and (ii) configured to produce a detector output signal in response to said secondary X-ray photon;

a displacement sensor configured to produce a displacement signal reflecting the distance between the surface of the semiconductor wafer and the X-ray detector array;

a position control unit coupled to receive said displacement signal and configured to produce a position control signal;

a sample stage upon which the semiconductor wafer is placed, wherein the sample stage is coupled to receive said position control signal and configured to position the semiconductor wafer relative to the incident beam of monochromatic primary X-ray photons in response to the position control signal; and

a computer system coupled to receive the detector output signal produced by each of said plurality of X-ray detectors.

12. The apparatus as recited in claim 11, wherein said at least one atom comprises a plurality of atoms.

13. The apparatus as recited in claim 12, wherein said plurality of atoms are associated with different elements.

14. The apparatus as recited in claim 11, wherein the detector output signal produced by each of said plurality of X-ray detectors is proportional to an energy level of said secondary X-ray photon.

15. The apparatus as recited in claim 11, wherein the beam of monochromatic primary X-ray photons is incident upon an exposed region of the surface of the semiconductor substrate, the particle is located within the exposed region, and the X-ray detector array is positioned adjacent to the exposed region.

16. The apparatus as recited in claim 11, wherein an angle of incidence formed between the incident beam of monochromatic primary X-ray photons and the surface of the semiconductor wafer, measured in the plane containing the beam of monochromatic X-ray photons and normal to the surface of the surface of the semiconductor wafer, is less than 0.2 degree.

17. The apparatus as recited in claim 11, wherein the X-ray source comprises a rotating anode.

18. The apparatus as recited in claim 17, wherein the rotating anode comprises tungsten.

19. The apparatus as recited in claim 11, wherein said plurality of X-ray detectors comprises an electronic area image sensor including a plurality of photosensor elements arranged to form a two-dimensional array upon a monolithic semiconductor substrate.

20. The apparatus as recited in claim 11, further comprising a sample chamber containing the X-ray detector array, the displacement sensor, and the sample stage, and wherein substantially all of the air molecules within the sample chamber are evacuated prior to and during use.

21. A method for determining the elemental composition and relative location of a particle located upon a surface of a semiconductor wafer, comprising the steps of:

positioning an array of X-ray detectors adjacent to the surface of the semiconductor wafer, wherein the array of X-ray detectors comprises a plurality of laterally displaced X-ray detectors, and each of the plurality of X-ray detectors is (i) oriented to receive a secondary X-ray photon emitted by at least one atom present within said particle, and (ii) configured to produce an output signal in response to said secondary X-ray photon;

exposing the surface of the semiconductor wafer to a beam of primary X-ray photons;

measuring and recording the output signal produced by each of the plurality of X-ray detectors comprising the array of X-ray detectors;

converting the recorded output signals to corresponding energy levels of detected X-ray photons;

forming a histogram representing the frequency distribution of the energy levels of detected X-ray photons;

using the characteristic energy levels corresponding to peaks in the histogram to identify the elemental composition of the particle;

searching the recorded output signals and the corresponding energy levels to determine the relative locations of X-ray detectors receiving secondary X-ray photons emitted by elements comprising the particle within the array of X-ray detectors; and

determining the relative location of the particle by mapping the relative locations of X-ray detectors receiving secondary x-ray photons emitted by elements comprising the particle to corresponding locations on the surface of the semiconductor wafer.

22. The method as recited in claim 21, wherein said at least one atom comprises a plurality of atoms.

23. The method as recited in claim 22, wherein said plurality of atoms are associated with different elements.

24. The method as recited in claim 21, wherein the output signal produced by each of said plurality of X-ray detectors is proportional to an energy level of said secondary X-ray photon.

25. The method as recited in claim 21, wherein the X-ray detectors comprising the array of X-ray detectors are arranged to allow two-dimensional resolution of the detected secondary X-ray photon emitted by the atom of the element present within the particle.

26. The method as recited in claim 25, wherein said plurality of X-ray detectors comprises an electronic area image sensor including a plurality of photosensor elements arranged to form a two-dimensional array upon a monolithic semiconductor substrate.

27. The method as recited in claim 21, wherein the beam of primary X-ray photons is incident upon an exposed region of the surface of the semiconductor wafer, the particle is located within the exposed region, and the X-ray detector array is positioned adjacent to the exposed region.

28. The method as recited in claim 21, wherein an angle of incidence formed between the incident beam of primary X-ray photons and the surface of the semiconductor wafer, measured in the plane containing the beam of primary X-ray photons and normal to the surface of the semiconductor wafer, is less than 0.2 degree.