Claims
- 1. A process for aligning the surface of a chosen member with the scan field of a focused beam of radiation or particles which includes the steps of:
- (a) providing a set of alignment marks on said surface of said member, said marks in said set being spaced at a predetermined periodicity;
- (b) providing a continuous back and forth scanning movement of said beam over said set of alignment marks at a predetermined and fixed velocity to produce a serial detection electrical signal that is indicative of the periodicity of spacing of said set of alignment marks and whose phase angle corresponds to the relative position of said set of alignment marks;
- (c) electronically processing said detection signal to generate an alignment signal comprising a fundamental periodic signal of a selected frequency;
- (d) providing a reference electrical signal comprising a periodic signal of said selected frequency and predetermined phase, said phase having a predetermined relationship to said scan field of said beam;
- (e) comparing the phase angle of said alignment signal and the phase angle of said reference signal and generating an error signal which is proportional to the phase difference of said alignment signal and said reference signal;
- (f) providing lateral relative movement between said scan field of said beam and said set of alignment marks in response to said error signal until said alignment signal and said reference signal become congruent in phase whereby highly accurate alignment of said surface of said chosen member with said scan field of said focused beam of radiation is produced.
- 2. The process set forth in claim 1 which includes, prior to said scanning movement between said beam and said set of alignment marks, coarsely aligning said beam and said set of alignment marks to within one period of the spacing between marks in said set of alignment marks.
- 3. The process set forth in claim 1 wherein said chosen member is a wafer of a selected semiconductor material.
- 4. The process set forth in claim 1 wherein said radiation is selected from the group consisting of ions, electrons, and a laser beam.
- 5. The process set forth in claim 1 wherein said set of alignment marks comprises a repetitive pattern of fine bars which form a grating structure.
- 6. The process set forth in claim 1 wherein said set of alignment marks comprises a two-dimensional array of fine dots of uniform and predetermined size, with adjacent dots being separated by a distance equal to the dot diameter.
- 7. The process set forth in claim 1 wherein said electronically processing said detection signal comprises passing said detection signal through a relatively narrow bandpass filter and through an amplifier tuned to said selected frequency.
- 8. The process set forth in claim 1 wherein said reference signal is generated by electronic circuitry comprising a sine wave generator.
- 9. The process set forth in claim 1 wherein said lateral relative movement is provided by mechanical motion of a platform supporting said chosen member.
- 10. The process set forth in claim 1 wherein said lateral relative movement is provided by controllably deflecting said focused beam of radiation.
- 11. The process set forth in claim 1 wherein:
- (a) said chosen member comprises a wafer of silicon;
- (b) said radiation comprises a beam of gallium ions at an energy of 60 kiloelectronvolts and a fluence of 1 ampere per centimeter, focused to a spot size of approximately 1500 angstoms;
- (c) said alignment marks comprise a repetitive pattern of fine bars forming a grating structure, the width of each of said bars being 0.15 micrometer and the spacing between adjacent said bars being 0.4 micrometer;
- (d) said scanning movement is at a velocity of approximately 6.8 millimeters per second;
- (e) said processing said detection signal comprises passing said detection signal through a relatively narrow bandpass filter and through an amplifier tuned to said selected frequency;
- (f) said reference signal is formed by a sine wave generator;
- (g) said lateral relative movement is provided by controllably deflecting said focused beam of radiation.
- 12. A process for aligning the surface of a first chosen member with the surface of a second chosen member which includes the steps of:
- (a) providing a first set of alignment marks on said surface of said first member and spaced at a predetermined periodicity;
- (b) providing a chosen fixed reference point for determining the relative positions of said first and said second chosen members;
- (c) generating from said first set of alignment marks a first detection signal comprising a serial electronic signal as a function of time and containing serial information corresponding to the position of said first set of alignment marks;
- (d) electronically processing said first detection signal to generate a first alignment signal with a high signal-to-noise ratio;
- (e) providing a first reference electrical signal comprising a periodic signal of a predetermined frequency and phase;
- (f) comparing the phase angle of said first alignment signal and the phase angle of said first reference signal and generating a first error signal proportional to the phase difference of said first alignment signal and said first reference signal;
- (g) providing lateral movement of said first set of alignment marks with respect to said chosen reference point in response to said first error signal until said first alignment signal and said first reference signal become congruent in phase, to produce accurate alignment of said surface of said first chosen member with said chosen reference point;
- (h) providing a second set of alignment marks on said surface of said second member and which is substantially identical to said first set of alignment marks;
- (i) generating from said second set of alignment marks a second detection signal comprising a serial electronic signal as a function of time and containing serial information corresponding to the position of said second set of alignment marks;
- (j) electronically processing said second detection signal to generate a second alignment signal with a high signal-to-noise ratio;
- (k) providing a second reference electrical signal comprising a periodic signal of predetermined frequency and phase;
- (l) comparing the phase angle of said second alignment signal and the phase angle of said second reference signal and generating a second error signal proportional to the phase difference of said second alignment signal and said second reference signal;
- (m) providing lateral movement of said second set of alignment marks with respect to said chosen reference point in response to said error signal until said second alignment signal and said second reference signal became congruent in phase, to produce accurate alignment of said surface of said second chosen member with said chosen reference point and thus produce accurate alignment of said surface of said first chosen member with said surface of said second chosen member.
- 13. The process set forth in claim 12 wherein said generating of said first or second detection signal comprises:
- (a) providing a source of incoherent flood radiation for illuminating said first or said second set of alignment marks, respectively;
- (b) illuminating said first or said second set of alignment marks with said flood radiation to produce reflected radiation therefrom;
- (c) imaging said reflected radiation onto an imaging detector means;
- (d) serially reading the image of said reflected radiation in said imaging detector means to generate said first or said second serial electronic signal as a function of time and containing said serial information.
- 14. The process set forth in claim 13 which includes, prior to said illuminating, coarsly aligning each of said first and second sets of alignment marks with respect to said chosen reference point to within one period of the spacing between marks in said first or second sets of alignment marks respectively.
- 15. The process set forth in claim 12 wherein said electronically processing said first or second detection signal comprises passing said first or second detection signal through a relatively narrow bandpass filter and through an amplifier tuned to a selected frequency.
- 16. A process for aligning the surface of a first chosen member with the surface of a second chosen member which includes the steps of:
- (a) providing a first set of alignment marks on said surface of said first member and spaced at a first predetermined periodicity;
- (b) providing a second set of alignment marks on said surface of said second member and spaced at a second predetermined periodicity which is different from said first predetermined periodicity;
- (c) providing a chosen fixed referenced point for determining the relative positions of said first and second chosen members;
- (d) generating from said first and said second sets of alignment marks a composite detection signal comprising a serial electronic signal as a function of time and containing serial information corresponding to the position of said first set of alignment marks and of said second set of alignment marks;
- (e) electronically processing said composite detection signal to generate a first alignment signal representing the position of said first set of alignment marks and a second alignment signal representing the position of said second set of alignment marks;
- (f) providing first and second reference electrical signals comprising periodic signals of predetermined frequency and phase;
- (g) comparing the phase angle of said first alignment signal with the phase angle of said first reference signal to generate a first error signal proportional to the phase difference of said first alignment signal and said first reference signal;
- (h) providing relative lateral movement of said first chosen member with respect to said chosen reference point in response to said error signal until said first alignment signal and said first reference signal become congruent in phase, to produce accurate alignment of said first chosen member with said chosen reference point;
- (i) comparing the phase angle of said second alignment signal with the phase angle of said second reference signal to generate a second error signal proportional to the phase difference of said second alignment signal and said second reference signal; and
- (j) providing relative lateral movement of said second chosen member with respect to said chosen reference point in response to said second error signal until said second alignment signal and said second reference signal become congruent in phase, to produce accurate alignment of said second chosen member with said chosen reference point and with said first chosen member.
- 17. The process set forth in claim 16 wherein said generating said composite detection signal comprises:
- (a) providing a source of incoherent flood radiation for illuminating said first and said second sets of alignment marks;
- (b) simultanteously illuminating said first and said second sets of alignment marks with said flood radiation, to produce reflected radiation therefrom;
- (c) imaging said reflected radiation onto an imaging detector means;
- (d) serially reading the image of said reflected radiation in said imaging detector means to generate said composite detection signal.
- 18. The process set forth in claim 13 or claim 17 wherein said flood radiation comprises radiation having a wavelength within the ultraviolet to far infrared range.
- 19. The process set forth in claim 12 or claim 16 wherein said first chosen member is a wafer of a selected semiconductor material and said second chosen member is a mask structure located above said wafer.
- 20. The process set forth in claim 12 or claim 16 wherein each of said first and second sets of alignment marks comprises a repetitive pattern of bars which form a grating structure.
- 21. The process set forth in claim 16 wherein said electronically processing said composite detection signal comprises passing said detection signal through two relatively narrow bandpass filters and through two corresponding amplifiers.
- 22. The process set forth in claim 16 wherein said lateral relative movement is provided by mechanical motion of a platform supporting said first member.
- 23. The process set forth in claim 16 wherein said lateral relative movement is provided by mechanical motion of a platform supporting said second member.
- 24. The process set forth in claim 1, 12 or 16 wherein:
- (a) said set of alignment marks is formed to have a selected coded periodicity;
- (b) said reference signal comprises an encoded signal with coding corresponding to said selected coded periodicity of said set of alignment marks; and
- (c) said comparing comprises correlating said alignment signal and said reference signal to generate said error signal which is indicative of the extent of correlation of said alignment signal and said reference signal in time.
Government Interests
The Government has rights in this invention pursuant to Contract No. N00123-78-C-0195 awarded by the Department of the Navy.
US Referenced Citations (10)
Non-Patent Literature Citations (1)
Entry |
"Optimal Patterns for Alignment" by Makaous Applied Optics, vol. 13, No. 3, Mar. 74, pp. 659-664. |