Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/88—Investigating the presence of flaws or contamination
  • G01N21/95—Investigating the presence of flaws or contamination characterised by the material or shape of the object to be examined
  • G01N21/956—Inspecting patterns on the surface of objects
  • G01N21/95607—Inspecting patterns on the surface of objects using a comparative method
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/88—Investigating the presence of flaws or contamination
  • G01N21/95—Investigating the presence of flaws or contamination characterised by the material or shape of the object to be examined
  • G01N21/9501—Semiconductor wafers

Definitions

• Semiconductor wafers must be scanned for defects both before any patterning is done and after patterning to identify sites with defects that would lead to a bad semiconductor device when the wafer is cut into chips.
• the problem of scanning becomes more difficult as the 4th power of the wafer diameter.
• Methods or strategies for improved scanning for defects thus become increasingly important in keeping the cost of inspection in line with the cost of patterning the wafers in the first place.
• rapid scanning of wafers and similar devices makes in-process scanning and process control a reality.
• the present invention is a systems approach to scanning wafers that makes use of several existing technologies that are used together in a unique way.
• a semiconductor wafer is centered on a vacuum chuck that is capable of being rapidly rotated about an axis normal to the wafer surface.
• the chuck is rotated and the surface scanned with an optical head that is the same as that used to scan compact disks (CD's) .
• the output of the read head is compared to a "golden standard" of what a perfectly patterned wafer should look like. Differences between the golden standard and the patterned wafer indicate flaws in the patterning. (In the case of an unpattemed wafer, the standard would show no signal and any signal from the read head would signify a flaw in the virgin wafer) .
• Fig. 1 illustrates the scanning apparatus of the present invention.
• Fig. 2 depicts the scanning apparatus of Fig. 1 incorporating a plurality of read heads.
• the scanning apparatus 10 of the present invention is depicted in Fig. 1.
• the apparatus includes a rotating vacuum chuck 20, an optical read head 30, a read head actuator and arm 40 and a processor 50.
• Mounted to vacuum chuck 20 is a planar device 60 which is to scan and evaluate by scanning apparatus 10.
• planar device 60 is a semiconductor wafer containing a plurality of semiconductor devices.
• the vacuum is supplied to the vacuum chuck 20 through a commercially available rotary coupling.
• the vacuum chuck 20 is necessary because semiconductor wafers 60 are out of flat in the free state to a degree sufficient to prevent rapid scanning. Even so, there is sufficient unevenness in the wafer surface 60 to require use of an automatic focus sensor 31 built into the CD read head 30. This sensor would cause the read head to be correctly positioned above the wafer using active feedback to an actuator thus keeping the read head in best focus at all times during the scanning.
• the output signal from the read head 30 is output on signal line 47 to processor 50 where it is compared with the golden standard.
• the rotating vacuum chuck 20 and the golden standard will be synchronized using a rotary encoder 25 on the rotating chuck 20.
• the output of rotary encoder 25 is input to processor 50 via signal line 27.
• the radial location of the CD read head 30 will be ascertained using a displacement or angular encoder 45 incorporated into the actuator 40.
• the combination of the rotary encoder 25 and lateral position encoder 45 permit the location on the surface 60 to be matched with the golden standard. This comparison between read head signal and golden standard would be made continuously by processor 50 as the read head 30 scans the wafer 60 from center to edge while the wafer rotates.
• Another means for obtaining synchronization is to scan or image the flats and notches on semiconductor wafers 60 and correlating the position of the flats with the azi uthal or rotary encoder 25 reading. This then would be synchronized with the golden standard to ensure the patterning was correctly positioned relative to the flats and notches.
• the wafer 60 is preferably well centered on the vacuum chuck 20, there will inevitably be small residual decanters. Since the pattern coincident with the axis of rotation will remain fixed as the chuck 20 rotates, there is a means of locating the read head 30 with the axis of rotation to the limit of lateral resolution of the read head 30. As the read head 30 is scanned outward from the center of the wafer 60, the amount of information to be compared with the golden standard is small. In this time period of scanning near the center of wafer 60, the residual decanter can be determined and the golden standard corrected to account for the once per revolution decentration or the lateral motion of the read head 30 actively controlled to match the noted residual decanter.
• the wafer 60 is scanned in a spiral manner just as a phonograph record or the CD, from center to edge, there will be a much higher rate of scanned information at the edge of the wafer 60 than the center.
• a second read head 30 1 is moved in and scans in an interlaced manner with respect to the first read head 30. As the heads 30, 30 1 move farther out, subsequent heads 30" would be brought in to scan in parallel with the first two, etc.
• the present invention is not limited to the scanning of semiconductor wafers.
• the method and apparatus have similar applicability to unpattemed wafers and other nominally featureless, near planar surfaces such as computer hard drives, flat panel displays and the glass substrates for LCD screens and the like. Any large area, flat, patterned surface could equally well be scanned by the approach of the present invention.
• the method can be used for in-process scanning and the results of the scanning used for process control. The scanning can be accomplished fast enough to permit near real time adjustment of patterning parameters to improve yields and correct defects.
• a preferred embodiment of the method of the present invention is for rapidly scanning semiconductor wafers 60 using a spiral scan such as is used on a phonograph or CD player. The method is faster than a raster scan because there is no starting and stopping of the motion.
• the method of the present invention can be used in connection with the following: The use of a rotating vacuum chuck 30 to hold the semiconductor wafer 60 flat during scanning.
• the sensor 31 output would drive an actuator 40 to hold the read head 30 in the best focus position using closed loop feed back just as is done on CD players.
• the use of a rotary encoder 25 on the spinning vacuum chuck to encode the azimuthal position of the semiconductor wafer 60 for the purposes of synchronization.
• variable rotary speed to even out the information variation from center to edge of the rotating wafer 60, running the speed faster when scanning near the center of the wafer 60.

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• Physics & Mathematics (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Biochemistry (AREA)
• General Health & Medical Sciences (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Investigating Materials By The Use Of Optical Means Adapted For Particular Applications (AREA)

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• 1998
  • 1998-02-20 WO PCT/US1998/003239 patent/WO1998037404A1/en active Search and Examination
  • 1998-02-20 EP EP98907527A patent/EP0961928A4/de not_active Withdrawn
  • 1998-02-20 JP JP53687398A patent/JP2001512576A/ja active Pending

Patent Citations (7)

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