US3928094A
Expired / Lapsed
US
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Method of aligning a wafer beneath a mask and system therefor and wafer having a unique alignment pattern
Assignee: Fairchild Semiconductor Corp
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Filing: 1975-01-16
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Granted: 1975-12-23
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Expires: 1995-01-16
Abstract
Abstract A method of aligning a wafer beneath a mask comprising forming a plurality of spaced-apart steps of predetermined length on a wafer such that the edges of the steps define a pattern of parallel lines, positioning the wafer beneath a mask having symmetrical openings spaced-apart by a distance substantially equal to the predetermined length such that the ends of the steps appear under the openings, illuminating the wafer with rays of light directed parallel to a plane perpendicular to the edges and incident upon the edges at an oblique angle relative to the top surface of the wafer, simultaneously detecting first diffraction scattered light emanating from one end of the steps and passing through one of the openings and second diffraction scattered light emanating from the other end of the steps and passing through the other of the openings, and moving the wafer relative to the mask until the first light has a predetermined relationship to the second light, and system therefor. In the preferred embodiment the steps form an alternating series of ridges and grooves. By remotely placing a second set of steps perpendicular to the direction of the first set, and a third set of steps parallel to the first set of steps, a complete and accurate alignment of the wafer beneath the mask is achieved. This method lends itself to aligning a unique semiconductor wafer that includes steps formed in a scribe channel separating a pair of adjacent chips.
Inventors
- 👤 James B Angell
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 12:11
CPC Classifications
G; G03; G03F; G03F9/00; G03F9/70; G03F9/7073; G03F9/7076; G03F9/7049; Y; Y10; Y10S; Y10S148/00; Y10S148/028; Y10S148/051; Y10S148/102; Y10S148/106; Y10S438/00; Y10S438/975
Claims Analysis
Total Claims: 23
Claim 1
Independent Claim
164 words
A METHOD OF ALIGNING A WAFER BENEATH A MASK COMPRISING: FORMING A FIRST PLURALITY OF SPACED-APART STEPS OF PREDETERMINED LENGTH ON A WAFER SUCH THAT THE EDGES OF SAID STEPS DEFINE A PATTERN OF PARALLEL LINES; POSITIONING THE WAFER BENEATH A MASK HAVING A FIRST SET OF SYMMETRICAL OPENINGS SPACED-APART BY A DISTANCE SUBSTANTIALLY EQUAL TO SAID PREDETERMINED LENGTH SUCH THAT THE ENDS OF SAID STEPS APPEAR UNDER SAID OPENINGS; ILLUMINATING THE WAFER WITH RAYS OF LIGHT DIRECTED PARALLEL TO A PLANE PERPENDICULAR TO SAID EDGES AND INCIDENT UPON SAID EDGES AT AN ABLIQUE ANGLE RELATIVE TO THE TOP SURFACE OF THE WAFER; SIMULATNEOUSLY DETECTING FIRST DIFFRACTION SCATTERED LIGHT EMANATING FROM ONE END OF SAID STEPS AND PASSING THROUGH ONE OF SAID OPENINGS AND SECOND DIFFRACTION SCATTERED LIGHT EMANATING FROM THE OTHER END OF SAID STEPS AND PASSING THROUGH THE OTHER OF SAID OPENINGS; AND MOVING THE WAFER RELATIVE TO THE MASK UNTIL SAID FIRST LIGHT HAS A PREDETERMINED RELATIONSHIP TO SAID SECOND LIGHT.
Claim 2
Independent Claim
164 words
A METHOD OF ALIGNING A WAFER BENEATH A MASK COMPRISING: FORMING A FIRST PLURALITY OF SPACED-APART STEPS OF PREDETERMINED LENGTH ON A WAFER SUCH THAT THE EDGES OF SAID STEPS DEFINE A PATTERN OF PARALLEL LINES; POSITIONING THE WAFER BENEATH A MASK HAVING A FIRST SET OF SYMMETRICAL OPENINGS SPACED-APART BY A DISTANCE SUBSTANTIALLY EQUAL TO SAID PREDETERMINED LENGTH SUCH THAT THE ENDS OF SAID STEPS APPEAR UNDER SAID OPENINGS; ILLUMINATING THE WAFER WITH RAYS OF LIGHT DIRECTED PARALLEL TO A PLANE PERPENDICULAR TO SAID EDGES AND INCIDENT UPON SAID EDGES AT AN ABLIQUE ANGLE RELATIVE TO THE TOP SURFACE OF THE WAFER; SIMULATNEOUSLY DETECTING FIRST DIFFRACTION SCATTERED LIGHT EMANATING FROM ONE END OF SAID STEPS AND PASSING THROUGH ONE OF SAID OPENINGS AND SECOND DIFFRACTION SCATTERED LIGHT EMANATING FROM THE OTHER END OF SAID STEPS AND PASSING THROUGH THE OTHER OF SAID OPENINGS; AND MOVING THE WAFER RELATIVE TO THE MASK UNTIL SAID FIRST LIGHT HAS A PREDETERMINED RELATIONSHIP TO SAID SECOND LIGHT.
Claim 3
Dependent Claim
49 words
A method of aligning a wafer beneath a mask as recited in claim 1 wherein said rays of light are collimated and substantially of single wavelength, and wherein said steps are formed so as to have a height that is of the same order of magnitude as said wavelength.
Claim 4
Dependent Claim
33 words
A method of aligning a wafer beneath a mask as recited in claim 2 wherein said steps are formed so as to have a height that is twice the magnitude of said wavelength.
Claim 5
Dependent Claim
31 words
A method of aligning a wafer beneath a mask as recited in claim 1 wherein said steps are formed so as to correspond to an alternating series of ridges and grooves.
Claim 6
Dependent Claim
222 words
A method of aligning a wafer beneath a mask as recited in claim 1 wherein the mask has a second set of symmetrical openings spaced apart by a distance substantially equal to said predetermined length and arranged substantially parallel to said first set and further including forming a second plurality of steps on the wafer such that the edges of said second steps define a pattern of parallEl lines that are spaced apart from and parallel to said parallel lines defined by said first steps, positioning the wafer beneath the mask such that the ends of said second steps appear under said second set of openings; illuminating the wafer with rays of light directed parallel to a plane perpendicular to the edges of said second steps and incident upon said edges at an oblique angle relative to the top surface of the wafer; simultaneously detecting third diffraction scattered light emanating from one of said second steps and passing through one of said second set of openings and fourth diffraction scattered light emanating from the other end of said second steps and passing through the other of said second set of openings; and moving the wafer relative to the mask until said third light has a predetermined relationship to said fourth light, thereby to prevent angular misalignment of the wafer beneath the mask.
Claim 7
Dependent Claim
232 words
A method of aligning a wafer beneath a mask as recited in claim 1 wherein the mask has a third set of symmetrical openings spaced apart by a distance substantially equal to said predetermined length and arranged substantially perpendicular to said first set and further including forming a third plurality of steps on the wafer such that the edges of said third steps define a pattern of parallel lines that are perpendicular to said parallel lines defined by said first step, positioning the wafer beneath the mask such that the ends of said third steps appear under said third set of openings; illuminating the wafer with rays of light directed parallel to a plane perpendicular to the edges of said third steps and incident upon said edges at an oblique angle relative to the top surface of the wafer; simultaneously detecting fifth diffraction scattered light emanating from one end of said third steps and passing through one of said third set of openings and sixth diffraction scattered light emanating from the other end of said third steps and passing through the other of said third set of openings; and moving the wafer relative to the mask until said fifth light has a predetermined relationship to said sixth light, thereby to prevent misalignment of the wafer beneath the mask in a direction normal to that defined by said edges of said third steps.
Claim 8
Dependent Claim
232 words
A method of aligning a wafer beneath a mask as recited in claim 5 wherein the mask has a third set of symmetrical openings spaced apart by a distance substantially equal to said predetermined length and arranged substantially perpendicular to said first set and further including forming a third plurality of steps on the wafer such that the edges of said third steps define a pattern of parallel lines that are perpendicular to said parallel lines defined by said first step, positioning the wafer beneath the mask such that the ends of said third steps appear under said third set of openings; illuminating the wafer with rays of light directed parallel to a plane perpendicular to the edges of said third steps and incident upon said edges at an oblique angle relative to the top surface of the wafer; simultaneously detecting fifth diffraction scattered light emanating from one end of said third steps and passing through one of said third set of openings and sixth diffraction scattered light emanating from the other end of said third steps and passing through the other of said third set of openings; and moving the wafer relative to the mask until said fifth light has a predetermined relationship to said sixth light, thereby to prevent misalignment of the wafer beneath the mask in a direction normal to that defined by said edges of said third steps.
Claim 9
Dependent Claim
43 words
A method of aligning a wafer beneath a mask as recited in claim 1 wherein the step of simultaneously detecting first diffraction scattered light includes focusing a pair of photodiodes on said first set of spaced-apart openings above said ends of said steps.
Claim 10
Dependent Claim
50 words
A method of aligning a wafer beneath a mask as recited in claim 1 and after simultaneously detecting first diffrAction scattered light, differentially amplifying respective signals derived from said first and second light so as to provide an indication of the misalignment of the wafer with respect to the mask.
Claim 11
Independent Claim
168 words
A method of aligning a wafer beneath a mask comprising: forming a first plurality of spaced-apart steps of predetermined length on a wafer such that the edges of said steps define a pattern of parallel lines; providing a mask having first and second openings defining centers spaced apart by a distance substantially equal to said predetermined length; positioning the wafer beneath said mask with the respective ends of said steps lying beneath said first and second openings; illuminating the wafer with rays of light directed parallel to a plane perpendicular to said edges and incident upon said edges at an oblique angle relative to the top surface of the wafer; simultaneously detecting first diffraction scattered light emanating from one end of said steps and passing through said first opening and second diffraction scattered light emanating from the other end of said steps and passing through said second opening; and moving the wafer relative to said mask until said first light has a predetermined relationship to said second light.
Claim 12
Independent Claim
168 words
A method of aligning a wafer beneath a mask comprising: forming a first plurality of spaced-apart steps of predetermined length on a wafer such that the edges of said steps define a pattern of parallel lines; providing a mask having first and second openings defining centers spaced apart by a distance substantially equal to said predetermined length; positioning the wafer beneath said mask with the respective ends of said steps lying beneath said first and second openings; illuminating the wafer with rays of light directed parallel to a plane perpendicular to said edges and incident upon said edges at an oblique angle relative to the top surface of the wafer; simultaneously detecting first diffraction scattered light emanating from one end of said steps and passing through said first opening and second diffraction scattered light emanating from the other end of said steps and passing through said second opening; and moving the wafer relative to said mask until said first light has a predetermined relationship to said second light.
Claim 13
Independent Claim
203 words
A method of aligning a wafer including a pair of adjacent chips that are separated by a scribe channel beneath a mask comprising the steps of: forming a first plurality of spaced-apart steps of predetermined length on a pair of adjacent chips which extend outwardly from the opposed edges of a scribe channel such that the edges of said steps define a pattern of parallel lines that are spaced apart by said channel; positioning the wafer beneath a mask having a bar that has a width that is uniform and dimensionally intermediate the distance between said edges of said channel and the outermost extremities of said steps over said channel and said adjacent chips such that the ends of said steps are exposed; illuminating the adjacent chips with rays of light directed parallel to a plane perpendicular to said edges and incident upon said edges at an oblique angle relative to the top surface of the wafer; simultaneously detecting first diffraction scattered light emanating from one end of said steps and second diffraction scattered light emanating from the other end of said steps; and moving the wafer relative to the mask until said first light has a predetermined relationship to said second light.
Claim 14
Independent Claim
203 words
A method of aligning a wafer including a pair of adjacent chips that are separated by a scribe channel beneath a mask comprising the steps of: forming a first plurality of spaced-apart steps of predetermined length on a pair of adjacent chips which extend outwardly from the opposed edges of a scribe channel such that the edges of said steps define a pattern of parallel lines that are spaced apart by said channel; positioning the wafer beneath a mask having a bar that has a width that is uniform and dimensionally intermediate the distance between said edges of said channel and the outermost extremities of said steps over said channel and said adjacent chips such that the ends of said steps are exposed; illuminating the adjacent chips with rays of light directed parallel to a plane perpendicular to said edges and incident upon said edges at an oblique angle relative to the top surface of the wafer; simultaneously detecting first diffraction scattered light emanating from one end of said steps and second diffraction scattered light emanating from the other end of said steps; and moving the wafer relative to the mask until said first light has a predetermined relationship to said second light.
Claim 15
Dependent Claim
63 words
A method of aligning a wafer including a pair of adjacent chips that are separated by a scribe channel beneath a mask as recited in claim 11 wherein said rays of light are collimated and substantially of a single wavelength, and wherein said steps are formed so as to have a height that is of the same order of magnitude as said wavelength.
Claim 16
Dependent Claim
43 words
A method of aligning a wafer including a pair of adjacent chips that are separated by a scribe channel as recited in claim 12 wherein said steps are formed so as to have a height that is twice the magnitude of said wavelength.
Claim 17
Dependent Claim
41 words
A method of aligning a wafer including a pair of adjacent chips that are separated by a scribe channel as recited in claim 11 wherein said steps are formed so as to correspond to an alternating series of ridges and grooves.
Claim 18
Dependent Claim
70 words
A method of aligning a wafer including a pair of adjacent chips that are separated by a scribe channel as recited in claim 11 wherein simultaneously detecting first scattered light includes focusing a pair of substantially matched photodiodes, each defining a detection window, on said exposed ends of said steps such that the inner edge of each said detection window is aligned with the respective outer edges of said bar.
Claim 19
Dependent Claim
53 words
A method of aligning a wafer including a pair of adjacent chips that are separated by a scribe channel as recited in claim 15 and further including differentially amplifying said first and second light so as to provide an error signal indicative of the misalignment of the wafer wIth respect to the mask.
Claim 20
Dependent Claim
58 words
A method of aligning a wafer including a pair of adjacent chips that are separated by a scribe channel as recited in claim 16 and after the step of differentially amplifying said first and second light, applying said error signal to an electromechanical wafer positioning means which is operative to move the wafer into alignment with the mask.
Claim 21
Dependent Claim
126 words
A method of aligning a wafer including a pair of adjacent chips that are separated by a scribe channel as recited in claim 11 and including forming a second mask over said scribe channel, said second mask including a bar portion which defines a number of serrations which number is mutually prime to the number of said plurality of steps, illuminating the adjacent chips with rays of light such that some of said light is scattered by diffraction off the exposed ends of said underlying first plurality of steps, simultaneously detecting third and fourth diffraction scattered light emanating from the respective ends of said steps, and moving the wafer relative to the second mask until said third light has a predetermined relationship to said fourth light.
Claim 22
Independent Claim
191 words
A system for aligning a wafer beneath a mask comprising: a wafer including a top surface having a plurality of scribe channels formed therein, at least one of said scribe channels formed to define a plurality of spaced-apart steps of a predetermined length such that the edges of said steps define a pattern of parallel lines; a mask having a set of symmetrical openings spaced apart by a distance substantially equal to said predetermined length, said mask being positioned above said top surface such that the ends of said steps appear under said openings; means for illuminating the wafer with rays of light directed parallel to a plane perpendicular to said edges and incident upon said edges at an oblique angle relative to said top surface; means for simultaneously detecting first diffraction scattered light emanating from one end of said steps and passing through one of said openings and second diffraction scattered light emanating from the other end of said steps and passing through the other of said openings; and means for moving said wafer relative to said mask until said first light has a predetermined relationship to said second light.
Claim 23
Independent Claim
191 words
A system for aligning a wafer beneath a mask comprising: a wafer including a top surface having a plurality of scribe channels formed therein, at least one of said scribe channels formed to define a plurality of spaced-apart steps of a predetermined length such that the edges of said steps define a pattern of parallel lines; a mask having a set of symmetrical openings spaced apart by a distance substantially equal to said predetermined length, said mask being positioned above said top surface such that the ends of said steps appear under said openings; means for illuminating the wafer with rays of light directed parallel to a plane perpendicular to said edges and incident upon said edges at an oblique angle relative to said top surface; means for simultaneously detecting first diffraction scattered light emanating from one end of said steps and passing through one of said openings and second diffraction scattered light emanating from the other end of said steps and passing through the other of said openings; and means for moving said wafer relative to said mask until said first light has a predetermined relationship to said second light.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1978-12-22 | 1979-06-23 | 1979-12-23 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-12-22 | 1983-06-23 | 1983-12-23 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-12-22 | 1987-06-23 | 1987-12-23 | $7700.00 | Window Closed / Lapsed |