Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F9/00—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically
  • G03F9/70—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically for microlithography
  • G03F9/7003—Alignment type or strategy, e.g. leveling, global alignment
  • G03F9/7023—Aligning or positioning in direction perpendicular to substrate surface
  • G03F9/7026—Focusing

Definitions

• the invention relates to a method for determining the focusing state of a projection optical system, with the aid of which an object is imaged in a projection plane, using measurement marks on the object and / or markings on the projection plane.
• a more detailed definition of the subject matter of the invention results from the preamble of claim 1.
• the invention further relates to a device for performing the method.
• the focus for the image transmission must be carried out with great care, especially if the projection surface is not absolutely flat, but has unevenness of approximately the same order of magnitude as the image elements themselves, that is to say in the region.
• the most accurate focusing of the image plane on the projection surface plays a decisive role for the sharpness of all image areas.
• a scanning device with a photodiode device and a rotating mirror acting as a scanner for obtaining signals which represent the intensity curve described.
• an image projected back from the projection plane is passed over a slit-shaped photodiode with the aid of the rotating mirror.
• tet which emits an electrical signal corresponding to the received light intensity.
• the corresponding signal initially rises and decreases again after a certain period of time. The image sharpness and thus the focus state of the device can be determined from the measured time values by appropriate signal processing.
• multiple mechanical displacement processes are to be avoided during the measurement process.
• existing aids should be able to be used, which are already available for other adjustment processes.
• Multiple mechanical displacement processes during the measurement process should also be avoided for reasons of time and accuracy.
• the precise focus position can be determined or corrected quickly, reliably and with considerably improved accuracy with the aid of a mechanical computation process that is easy to control and easy to carry out. Aids are largely used, which are usually available or are required, for example for horizontal adjustment. This avoids extensive additives and measures, as are necessary in known methods or devices for fine focusing. The setting accuracy was considerably improved with the present method.
• the process can be used without restriction in production. It is noticeably faster and nevertheless more precise than previously known methods. Separate auto-calibration fields, as are required in known methods, are avoided in the present method, as a result of which the possible uses are broadened or the application is simplified.
• the following exemplary embodiments are described in connection with the production of semiconductor circuits from prepared semiconductor wafers.
• this application is only one example from a large number of technically similar applications. The example chosen is therefore not to be interpreted as a restriction of the various application possibilities of the invention.
• the results from the sampled values for the intensity profile of the images of an object are used as a criterion for a comparison operation between two sharpness signals derived from the intensity profile.
• the automatic refocusing is carried out by adjusting the projection optics and / or the projection plane and / or the object plane.
• projection optics 10 are provided, which direct an image of the projection surface 1 into a detector device 11.
• the detector device 11 contains a rotating mirror 12 which acts as a scanner and to which a beam splitter 13 is arranged.
• the beam splitter divides the information coming from the projection surface 1 into two beam paths A and B.
• the information is projected in the beam path A from the projection surface 1 into the image plane of a photoelectric detector arrangement 14, which is not exactly in the focal plane, but a certain distance behind the focal plane B1.
• the second beam path B the information is projected from the projection surface into an image plane of a second photoelectric detector arrangement 15, which likewise is not exactly in the focal plane, but this time somewhat in front of the focal plane B2 (in both cases in the direction of the beam path).
• the invention provides that Select focus position Z / F at the intersection X of both curves S 1 and S "according to FIG. 3 as a criterion for the optimal focus position.
• the projection surface 1 and / or the projection optics 10 and / or, if appropriate, the object plane 20 are adjusted parallel to the optical axis until the desired zero balance is reached.
• the control signal compensating the focus position can be obtained in different ways after determining the focus position Z / F at the curve intersection X of the two signals S 'and S ".
• the correction signal can be defined in accordance with the actual displacement of one of the two detector planes, if the other detector position is kept constant.
• the ideal focus position is reached when the intersection point X of the two curves S 'and S "lies within a predetermined tolerance range Y2-Y1 of the signal amplitudes.
• the sharpness signal difference can be used directly to derive a control signal.
• the described method can be used for the transfer of the image of a mask to a semiconductor wafer surface.
• An image of the mask is projected from a mask 20 via the optics 10 onto the wafer surface acting as projection surface 1 and then back-projected from the wafer surface via the optics 10, a semi-transparent mirror 25 and the scanner 12 into the detector device 11.
• the scanning of the intensity signals by the detector arrangements 14 and 15 and the further signal processing for deriving suitable control or correction signals for the focus adjustment is otherwise carried out according to the previously described method.
• the detector arrangement described and the evaluation of the intensity signals in the manner described allow the construction effort for the scanning or correction devices to be greatly reduced compared to known methods or devices.
• the accuracy of the focus setting is significantly increased due to the improved determination of the criterion for the zero adjustment.

Landscapes

• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Automatic Focus Adjustment (AREA)
• Exposure And Positioning Against Photoresist Photosensitive Materials (AREA)

Applications Claiming Priority (2)

Publications (1)

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Citations (3)

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• 1986
  • 1986-07-12 CH CH279386A patent/CH672376A5/de not_active IP Right Cessation
  • 1986-10-10 DE DE19863634609 patent/DE3634609A1/de not_active Ceased
  • 1986-12-01 WO PCT/CH1986/000167 patent/WO1988000720A1/de unknown

Patent Citations (3)

Non-Patent Citations (1)

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