Automatic visual inspection system for microelectronics

• US 3,909,602 A
• Filed: 09/27/1973
• Issued: 09/30/1975
• Est. Priority Date: 09/27/1973
• Status: Expired due to Term

• Current Assignee: Ernest Z. Micka
• Original Assignee: Ernest Z. Micka
• Inventors: Micka, Ernest Z.
• Primary Examiner(s): Gruber, Felix D.
• Application Number:
  US05/401,224
• Time in Patent Office: 733 Days
• Field of Search: 235/151.3 356/158,159,160,163,165,168,204,212,209,222,229,237,238 340/146.3Q,146.3G 250/556,557,562,563,572
• US Class Current: 716/136
• CPC Class Codes: G01N 21/95607 using a comparative method
• CPC Class Codes: G01R 31/308 using non-ionising electromagnetic radiation, e.g. optical radiation investigating or analysing materials by the use of optical means G01N21/00; image analysis G06T7/00

Abstract

A system for automatically inspecting an integrated circuit, including a device for shining a scanning narrow light beam at an integrated circuit to be inspected and another light beam at an accepted integrated circuit, a pair of photo-detectors that receive light reflected from these integrated circuits, and a comparing system compares the outputs of the photo-detectors.

Claims

1. In apparatus for inspecting a microelectronic circuit by directing a narrow light beam through a scanning device so that the light beam describes a predetermined scanning raster pattern at the microelectronic circuit, and detecting the reflected light, the improvement comprising means for splitting the light emerging from the scanning device into two light beam components that travel in two different directions;

first and second circuit holding means respectively positioned in the paths of the two beam components, for respectively holding a reference microelectronic circuit device and a test microelectronic circuit device to be inspected;

first and second light detectors;

means for directing light reflected from the surface of each microelectronic circuit device in response to being scanned by said light beam components, onto a different one of the light detectors, each light detector producing output signals representative of the light reflected from elemental areas of said surfaces; and

comparing means connected to the two light detectors for comparing said output signals and producing an output indicative of said comparison.

2. The improvement described in claim 1 wherein said splitting means produces component beams of mutually perpendicular directions of polarization, and recombines the component beams after they have been reflected from the two microelectronic circuit devices, into an emerging beam;

and said directing means includes a second polarizing beamsplitter positioned between the splitting means and the light detectors for splitting the emerging beam into two resplit beam components of mutually perpendicular directions of polarization and for directing each of the two resplit beam components onto a different one of the light detectors.

3. In apparatus as recited in claim 1 wherein said comparing means comprises means responsive to the output signals from said first and second light detectors for respectively generating a first function signal representative of the function

4. In apparatus as recited in claim 3 wherein said means for generating said first function signal includes means for subtracting the output signals of said first and second light detectors to produce a first difference signal, means for multiplying the output signal of said first detector with said first difference signal to produce a first product signal, means for squaring said first difference signal to produce a first squared signal, means for squaring the output signal of said first detector to produce a second squared signal, means for integrating said first squared signal to produce a first integrated signal, means for integrating said second squared signal to produce a second integrated signal, means for integrating said first product signal to produce a third integrated signal, means for multiplying said first and second integrated signals to produce a second product signal, means for squaring said third integrated signal to produce a third squared signal, and means for dividing said third squared signal by said second product signal to produce said first function signal.

5. In apparatus as recited in claim 4 wherein said means for generating said second function signal includes means for squaring the output signal of said second light detector to provide a fourth squared signal, means for multiplying said first difference signal with the output signal of said second light detector to provide a third product signal, means for integrating said fourth squared signal to produce a fourth integrated signal, means for integrating said third product signal to produce a fifth integrated signal, means for multiplying said first integrated signal with said fourth integrated signal to produce a fourth product signal, means for squaring said fifth integrated signal to produce a fifth squared signal, and means for dividing said fourth product signal by said fifth squared signal to produce said second function signal.

6. In apparatus for inspecting a microelectric circuit by directing a narrow light beam through a scanning device so that the light beam describes a predetermined scanning raster pattern at the microelectronic circuit and detecting the reflected light, the improvement comprising means for splitting the light emerging from the scanning device into two light beam components that travel in two different directions;

a circuit holding means positioned in the path of one of said beam components for holding a test microelectronic circuit device to be inspected;

a mask having a pattern which is acceptable and substantially identical to that of a test microelectronic circuit device to be inspected;

means for holding said mask in the path of the other of said beam components, first and second light detectors;

means for directing light reflected from the surface of said test microelectronic circuit device and said mask, in response to being scanned by said light beam components, onto a different one of the light detectors, each light detector producing output signals representative of the light reflected from elemental areas of said surfaces; and

comparing means connected to the two light detectors for comparing said output signals and producing an output indicative of said comparison.

7. Apparatus for inspecting a microelectronic circuit comprising light generating means for generating a first light beam a first polarizing beamsplitter means for prOducing second and third mutually perpendicularly polarized light beams in response to an impinging first light beam;

light directing means for directing said first light beam at said first polarizing beamsplitter means;

first and second circuit holders for respectively holding a reference microelectronic circuit and a test microelectronic circuit which is to be inspected;

means disposed between said first polarizing beamsplitter and each circuit holder for directing a different one of the polarized light beams on a corresponding microelectronic circuit and for directing the light beam back to the beamsplitter after reflection by the circuit, the beamsplitter being operative to recombine the two light beams;

a quarter wave retardation plate interposed in the path of each light beam between said first polarizing beamsplitter and said respective first and second circuit holders, a second polarizing beamsplitter positioned in the path of the recombined beam which emerges from the first beamsplitter, for splitting the recombined beam into fourth and fifth beams;

a pair of light detectors positioned to receive the fourth and fifth beams, for generating representative electrical signals; and

comparing means connected to the two light detectors for comparing their outputs and producing an indication of said comparison.

8. The apparatus described in claim 7 wherein said light directing means includes scanning mirror means for deflecting the light beam from the light generating means within a range of angles, and a parabolic mirror positioned between the scanning means and the first polarizing beamsplitter for orienting light from the scanning means so it travels along a path parallel to a predetermined optical axis, said scanning mirror being positioned at the focus of the parabolic mirror.

9. Apparatus as recited in claim 7 wherein said comparing means comprises means responsive to the output signals from said first and second light detectors for respectively generating a first function signal representative of the function

10. A system for comparing the surface of a test chip with a reference chip comprising means for generating a first and a second light beam, including means for moving said first and second light beams in a scanning pattern, and means for respectively directing said first and second light beams in said scanning pattern at said test chip and reference chip, whereby a first reflectance beam is reflected from the surface of the test chip and a second reflectance beam is reflected from the surface of said reference chip, a first and a second photo-detector, means for respectively directing said first and second reflectance beams at said first and second photodetectors which respectively produce first and second output signals responsive thereto, means responsive to said first and second output signals for respectively generating a first function signal representative of the function

11. In a system for comparing the surface of a test chip with a reference chip by shining two scanning light beams at their respective surfaces to respectively produce a first and second reflectance beam, an improved comparing system, comprising a first and a second photo-detector, means for respectively directing said first and second reflectance beams at said first and second photodetectors which respectively produce first and second output signals responsive thereto, means responsive to said first and second output signals for respectively generating a first function signal representative of the function

12. In apparatus as recited in claim 11 wherein said means for generating said first function signal includes means for subtracting the output signals of said first and second light detectors to produce a first difference signal, means for multiplying the output signal of said first detector with said first difference signal to produce a first product signal, means for squaring said first difference signal to produce a first squared signal, means for squaring the output signal of said first detector to produce a second squared signal, means for integrating said first squared signal to produce a first integrated signal, means for integrating said second squared signal to produce a second integrated signal, means for integrating said first product signal to produce a third integrated signal, means for mutiplying said first and second integrated signals to produce a second product signal, means for squaring said third integrated signal to produce a third squared signal, and means for dividing said third squared signal by said second product signal to produce said first function signal.

13. In apparatus as recited in claim 11 wherein said means for generating said second function signal includes means for squaring the output signal of said second light detector to provide a fourth squared signal, means for multiplying said first difference signal with the output signal of said second light detector to provide a third product signal, means for integrating said fourth squared signal to produce a fourth integrated signal, means for integrating said third product signal to produce a fifth integrated signal, means for multiplying said first integrated signal with said fourth integrated signal to produce a fourth product signal, means for squaring said fifth integrated signal to produce a fifth squared signal, and means for dividing said fourth product signal by said fifth squared signal to produce said second function signal.

14. In a system for comparing the surface of a test chip with a reference chip by shining two scanning light beams at their respective surfaces to respectively produce a first and second reflectance beam, an improved comparing method comprising generating a first and a second signal responsive to said first and second reflectance beams, subtracting said first and second signals to produce a first difference signal, multiplying said first signal with said first difference signal to produce a first product signal, squaring said first difference signal to produce a first squared signal, squaring said first signal to produce a second squared signal, integrating said first squared signal to produce a first integrated signal, integrating said second squared signal to produce a second integrated signal, integrating said first product signal to produce a third integrated signal, multiplying said first and second integrated signals to produce a second product signal, squaring said third integrated signal to produce a third squared signal, dividing said third squared signal by said second product signal to produce a first function signal, squaring the second signal to provide a fourth squared signal, multiplying said first difference signal with the second signal to provide a third product signal, integrating said fourth squared signal to produce a fourth integrated signal, integrating said third product signal to produce a fifth integrated signal, multiplying said first integrated signal with said fourth integrated signal to produce a fourth product signal, squaring said fifth integrated signal to produce a fifth squared signal, dividing said fourth product signal by said fifth squared signal to produce a second function signal, and subtracting said first function signal from said second function signal to produce a signal indicative as to whether said test chip compares favorably with said reference chip.

15. Apparatus as recited in claim 8 wherein there is respectively positioned a first and a second partial light transmitting, partial light reflective mirror in the path of each light beam between the respective quarter wave retardation plates and said first polarizing beamsplitter, and viewing means positioned to receive the partially reflected light from said first and second partial light transmitting, partial light reflecting mirrors to permit viewing of said reference and test microelectronic circuits while they are being scanned.