Particle position correlator and correlation method for a surface scanner

• US 4,641,967 A
• Filed: 10/11/1985
• Issued: 02/10/1987
• Est. Priority Date: 10/11/1985
• Status: Expired due to Term

• Current Assignee: Hughes Danbury Optical Systems Incorporated
• Original Assignee: Tencor Instruments (KLA Corporation)
• Inventors: Pecen, Jiri
• Primary Examiner(s): LaRoche, Eugene R.
• Assistant Examiner(s): Pascal, Robert J.
• Application Number:
  US06/786,620
• Time in Patent Office: 487 Days
• Field of Search: 356/237, 356/398, 250/492.2, 250/562, 250/563, 250/572, 358/106, 364/491
• US Class Current: 356/237.3
• CPC Class Codes: G01N 21/94 Investigating contamination, e.g. dust G01N21/85 takes precedence

Abstract

A method and apparatus for particle detection and position correlation that fuses separate detections of the same particle on adjacent scan lines into one. A first scan line on a surface is scanned with a laser beam and the scattered light detected. The detection generates address and amplitude data for each particle which is stored. The second line scanned also generates data which is stored in a buffer. Particle data between scan lines is compared. Data for new particles is stored, data for previous particles no longer detected being sent to computer storage, and data for the same particle being compared and only the one with larger amplitude being kept. The results in computer storage may be displayed as a wafer with those pixels lit which have particles.

Claims

1. claims

3. The process of claim 1 further comprising counting between step (d) and step (e) the number of scan lines with a particular Y-address corresponding to a particular particle detection, said previous data being sent in step (f) only when said number of scan lines counted is in a preset range, said previous data lacking a corresponding current datum with a matching Y-address being discarded when said number of scan lines counted is outside said preset range.

5. The process of claim 1 further comprising displaying said data in computer storage or a grid of pixels, said pixels having a characteristic dimension substantially larger than said separation between succeeding scan lines, a pixel being lit when at least one address corresponding to a pixel is in computer storage.

2. A process of particle detection and position correlation comprising,

(a) scanning a first scan line on a surface with a laser beam having a characteristic beam width, scattering of said laser beam from said surface being detected when a scattering amplitude is above a threshold value, a Y-address of said scanning beam being generated during said scanning,

(b) storing data from said scanning of said first line, as previous data, said data identifying an address having a scan line number and a Y-address, said data also including scattering amplitude data at each said address,

(c) scanning a second line with said laser beam, said second scan line being spaced a distance less than the beam width from said first scan line, scattering of said beam again being detected, data from said scanning of said second line being stored as current data,

(d) comparing said current data with said previous data, current data that lack a corresponding previous datum with a matching Y-address being stored as previous data, said current data having a corresponding previous datum with a matching Y-address replacing said previous datum when said amplitude data of said current data has a value larger than that of said previous datum,

(e) sending previous data that lack a corresponding current datum with a matching Y-address to a computer storage, and

(f) repeating steps (c)-(e) for third, fourth and succeeding scan lines until the entire surface is scanned.

4. The process of claim 2 wherein said preset range has a lower limit of two corresponding to noise and an upper limit of twelve corresponding to a surface line.

6. The process of claim 4 further comprising enlarging at least one of said lit pixels, said pixel having a plurality of subelements, each subelement corresponding to an address, a subelement being lit when said corresponding address is in computer storage.

8. The particle position correlator of claim 6 wherein said receiving means comprises an input buffer receiving amplitude data relating to a current scan line from a light detector in a surface scanner, said input buffer connected to said storing means storing said addresses and data and to said comparing means.

9. The particle position correlator of claim 6 wherein said sending means comprises a FIFO stack connected on an input end to said comparing means, and an output buffer connected to an output end of said FIFO stack to receive addresses and data to be sent and connected via an external bus to a computer storage.

10. The particle position correlator of claim 6 further comprising a means for counting the number of scan lines with a particular address corresponding to a particle detection, said addresses and data stored from previous scan lines that lack a matching address relating to a current scan line being discarded when the number of scan lines counted for said addresses is outside a preset range.

11. The particle position correlator of claim 9 wherein said preset range has a lower limit of two corresponding to noise and an upper limit of twelve corresponding to a detected surface line.

12. The particle position correlator of claim 6 wherein said addresses comprise a scan line number and a sweep clock count.

14. The particle position correlator of claim 12 wherein said preset range has a lower limit of two corresponding to noise and an upper limit of twelve corresponding to a detected surface line.

7. A particle position correlator for use in a surface scanner comprising,

means for receiving addresses and corresponding scattering amplitude data relating to particle detection on a current scan line,

means for storing said addresses and data, some of said addresses matching addresses stored from previous scan lines, the rest of such addresses corresponding to new particle detections,

means for comparing said addresses and said amplitude data relating to said current scan line with said addresses and corresponding amplitude data stored from said previous scan lines, said amplitude data being compared when said compared addresses match, one of said compared amplitude data having a larger amplitude value being stored in said storing means with the address to which said one corresponds, the other of said compared amplitude data and the address to which the other corresponds being discarded, and

means for sending said addresses and data stored from previous scan lines that lack a matching address relating to said current scan line to an output for computer storage, said sent addresses and data corresponding to finished particle detections.

13. A particle position correlator for use in a surface scanner comprising,

an input buffer receiving scattering amplitude data relating to particle detection on a current scan line from a light detector in a surface scanner and receiving addresses corresponding to said data, each of said addresses including at least a scan line number and a Y-address,

means connected to said input buffer for storing said addresses and data, some of said addresses matching addresses stored in said storing means from previous scan lines, the rest of said addresses corresponding to new particle detections,

means connected to said input buffer and to said storing means for comparing said addresses and said corresponding amplitude data relating to said current scan line with said addresses and corresponding amplitude data stored in said storing means from said previous scan lines, said corresponding amplitude data being compared when said compared addresses have matching Y-addresses, one of said compared amplitude data having a larger amplitude value being stored in said storing means with the address to which said one corresponds, the other of said compared amplitude data and the address to which said other corresponds being discarded,

means for counting the number of scan lines with a particular Y-address corresponding to each particle detection,

a FIFO stack connected at an input end to said comparing means, and an output buffer connected to an output end of said FIFO stack and connected via an external bus to a computer storage, said addresses and data stored from previous scan lines that lack a matching Y address relating to a current scan line being sent to said computer storage via said FIFO stack and said output buffer when the number of scan lines counted for said particular Y-address is in a preset range, and being discarded when the number of scan lines counted for said particular Y-address is outset said preset range.