U.S. patent number 3,900,736 [Application Number 05/437,585] was granted by the patent office on 1975-08-19 for method and apparatus for positioning a beam of charged particles.
This patent grant is currently assigned to International Business Machines Corporation. Invention is credited to Michel S. Michail, Ollie C. Woodard, Hannon S. Yourke.
United States Patent |
3,900,736 |
Michail , et al. |
August 19, 1975 |
Method and apparatus for positioning a beam of charged
particles
Abstract
A beam of charged particles is stepped from one predetermined
position to another to form a desired pattern on a semiconductor
wafer to which the beam is applied in accordance with a
predetermined pattern. Instead of the beam being stepped to each of
the predetermined positions, there is a dynamic correction for the
deviation of the actual position from its predetermined position so
that the beam is applied to the deviated position rather than the
predetermined position whereby the pattern is written within the
boundaries of the writing field as determined by the location of
four registration marks, which are in four separate positions or
points in the field. Through location of each of the four
registration marks, the writing field is precisely defined. Writing
fields may be interconnected by the sharing of registration marks
enabling the construction of chips which are larger than a single
writing field.
Inventors: |
Michail; Michel S. (Wappingers
Falls, NY), Woodard; Ollie C. (Poughkeepsie, NY), Yourke;
Hannon S. (New York, NY) |
Assignee: |
International Business Machines
Corporation (Armonk, NY)
|
Family
ID: |
23737046 |
Appl.
No.: |
05/437,585 |
Filed: |
January 28, 1974 |
Current U.S.
Class: |
250/492.2;
101/485; 219/121.26; 219/121.29; 219/121.3 |
Current CPC
Class: |
H01J
37/147 (20130101); H01J 37/3045 (20130101) |
Current International
Class: |
H01J
37/147 (20060101); H01J 37/30 (20060101); H01J
37/304 (20060101); H01J 037/00 () |
Field of
Search: |
;250/492A,398 ;219/121EB
;148/1.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Church; Craig E.
Attorney, Agent or Firm: Leach, Jr.; Frank C. Galanthay;
Theodore E.
Claims
What is claimed is:
1. A method of positioning a beam of charged particles
comprising:
ascertaining the actual location and shape of a four-sided area of
a target in which the beam is to be applied relative to the
location and shape of a design four-sided area;
directing the beam over the target after ascertaining the actual
location of the area of the target and its shape relative to the
location and shape of the design area;
and moving the beam in a predetermined path ot each of a plurality
of predetermined positions within the design area in accordance
with a predetermined pattern while dynamically electronically
compensating at each of the predetermined positions for the
deviation of the actual position within the actual area from the
predetermined position due to the actual area having a different
location and shape relative to the location and shape of the design
area to cause the beam to be shifted from the predetermined
position and applied at the deviated actual position so that a
pattern is written within the actual area in accordance with the
predetermined pattern.
2. The method according to claim 1 in which compensation at each of
the predetermined positions for the deviation of the actual
position from the predetermined position is obtained by
simultaneously deflecting the beam in orthogonal directions.
3. The method according to claim 2 in which the location and shape
of the area of the target is ascertained by scanning each of the
four corners of the area of the target separately with the
beam.
4. The method according to claim 3 in which the target is a
semiconductor wafer.
5. The method according to claim 2 in which:
the beam is moved in the predetermined path by simultaneously
deflecting the beam is orthogonal directions through the use of a
separate deflection voltage for each of the orthogonal
directions;
and obtaining the dynamic electronic compensation at each of the
predetermined positions for the deviation of the actual position
from the predetermined position by modifying the orthogonal
deflection voltages for deflecting the beam to the predetermined
position in each of the orthogonal directions in accordance with
the location and shape of the actual area relative to the location
and shape of the design area to obtain the compensating deflection
of the beam in each of the orthogonal directions.
6. The method according to claim 1 in which the location and shape
of the area of the target is ascertained by scanning each of the
four corners of the area of the target separately with the
beam.
7. The method according to claim 6 in which the target is a
semiconductor wafer.
8. The method according to claim 1 in which the target is a
semiconductor wafer.
9. The method according to claim 8 including:
writing a different predetermined pattern at different levels of
the wafer at different times through directing the beam over the
design area after each level of the wafer is formed;
and moving the beam in a predetermined path to each of a plurality
of predetermined positions within the design area in accordance
with the predetermined pattern at each of the levels while
dynamically electronically compensating at each of the
predetermined positions for the deviation of the actual position
within the actual area from the predetermined position due to the
actual area having a different location and shape relative to the
location and shape of the design area to cause the beam to be
shifted from the predetermined position and applied at the deviated
actual position so that a pattern is written within the actual area
in accordance with the predetermined pattern at each of the
levels.
10. A method of writing a continuous pattern in more than one
contiguous four-sided area of a target with a beam of charged
particles including:
ascertaining the actual location and shape of a first foursided
area of the target relative to the location and shape of a first
design four-sided area;
applying the beam to the first actual area to write the portion of
the continuous pattern therein in accordance with the actual
location and shape of the first actual area relative to the
location and shape of the first design area;
ascertaining the actual location and shape of a second foursided
area of the target having a boundary common with the first actual
area of the target relative to the location and shape of a second
design four-sided area;
and applying the beam to the second actual area to write the
portion of the continuous pattern therein in accordance with the
actual location and shape of the second actual area relative to the
location and shape of the second design area so that the pattern
forms a continuation across the common boundary between the first
and second actual areas.
11. The method according to claim 10 in which the location and
shape of each of the areas of the target is ascertained by scanning
each of the four corners of the area of the target with the
beam.
12. The method according to claim 11 in which the target is a
semiconductor wafer.
13. The method according to claim 10 in which the target is a
semiconductor wafer.
14. The method according to claim 13 including applying the beam to
each of the first and second actual areas after formation of
another level of the wafer to form another continuous pattern at
the another level.
15. An apparatus for controlling the movement of a beam of charged
particles comprising:
means to ascertain the actual location and shape of an area of a
target relative to the location and shape of a design area of the
target;
means to move the beam over the design area in a predetermined path
to each of a plurality of predetermined positions within the design
area in accordance with a predetermined pattern;
and means to shift the beam from the predetermined position within
the design area in accordance with the deviation of the actual
position within the actual area from the corresponding
predetermined position due to the actual area having a different
location and shape relative to the location and shape of the design
area to cause the beam to be applied at the actual position rather
than the corresponding predetermined position when the beam is
moved by said beam moving means for positioning at the
corresponding predetermined position.
16. The apparatus according to claim 15 in which:
said shifting means includes:
means to produce a signal in accordance with the deviation of each
of the actual positions from the corresponding predetermined
position;
means to deflect the beam from the predetermined position to the
actual position;
and means to supply the signal from said producing means to said
deflection means.
17. The apparatus according to claim 16 in which:
said producing means includes:
first means to produce a first signal in accordance with the
deviation of the actual position from the corresponding
predetermined position in a first direction;
and second means to produce a second signal in accordance with the
deviation of the actual position from the corresponding
predetermined position in a second direction that is perpendicular
to the first direction.
18. The apparatus according to claim 17 in which:
said first means of said producing means produces the first signal
dependent on the deflection signals supplied to said beam moving
means to move the beam in each of the first and second directions
to the predetermined position;
and said second means of said producing means produces the second
signal dependent on the deflection signals supplied to said beam
moving means to move the beam in each of the first and second
directions to the predetermined position.
19. The apparatus according to claim 15 including:
means to store information containing each of a plurality of
patterns for different levels of a semiconductor wafer forming the
design area;
said beam moving means moving the beam to a plurality of
predetermined positions within the design area at each of the
different levels of the wafer in accordance with the pattern for
the particular level after each level is formed;
said storing means supplying the stored information to said beam
moving means for the plurality of predetermined positions within
the design area to which the beam is to be moved in accordance with
the pattern for the particular level;
and said shifting means shifting the beam to each of the actual
positions within the actual area from the corresponding
predetermined position within the design area.
20. The apparatus according to claim 15 in which said shifting
means is separate from said beam moving means.
21. The apparatus according to claim 15 in which said deflection
means is separate from said beam moving means.
22. An apparatus for writing a continuous pattern with a beam of
charged particles in more than one contiguous four-sided area of a
target including:
means to move the beam over the target;
first means to control said moving means to move the beam to
ascertain the actual location and shape of a first four-sided area
relative to the location and shape of a first design four-sided
area;
said first means including means to control said moving means to
move the beam over the first design area in accordance with a
predetermined pattern;
second means to shift the beam from a predetermined position within
the first design area in accordance with the predetermined pattern
to its actual deviated position within the first actual area to
write a portion of the pattern, as defined by the predetermined
pattern, in the first actual area in accordance with the actual
location and shape of the first actual area relative to the
location and shape of the first design area;
said first means controlling said moving means to move the beam to
ascertain the actual location and shape of a second area relative
to the location and shape of a second design area with the second
actual area having a common boundary with the first actual
area;
said control means of said first means controlling said moving
means to move the beam over the second design area in accordance
with the predetermined pattern;
and said second means shifting the beam from a predetermined
position within the second design area to its actual deviated
position with the second actual area to write a portion of the
pattern within the second actual area in accordance with the actual
location and shape of the second actual area relative to the
location and shape of the second design area so that the pattern
forms a continuation across the common boundary between the first
and second actual areas.
23. The apparatus according to claim 22 in which the target is a
semiconductor wafer.
24. The apparatus according to claim 22 in which said first means
includes means to scan each of the four corners of each of the
areas of the target to be located with the beam so as to ascertain
the location and shape of each of the areas of the target to be
located in accordance with the location of the four corners of the
area of the target to be located.
25. A method of positioning a beam of charged particles
comprising:
ascertaining the actual location and shape of an area of a target
in which the beam is to be applied relative to the location and
shape of a design area;
directing the beam over the target after locating the actual area
of the target and its shape relative to the location and shape of
the design area;
and moving the beam in a predetermined path to each of a plurality
of predetermined positions within the design area in accordance
with a predetermined pattern while dynamically electronically
compensating at each of the predetermined positions for the
deviation of the actual position within the actual area from the
predetermined position due to the actual area having a different
location and shape relative to the location and shape of the design
area to cause the beam to be shifted from the predetermined
position and applied at the deviated actual position so that a
pattern is written within the actual area in accordance with the
predetermined pattern.
26. The method according to claim 25 in which compensation at each
of the predetermined positions for the deviation of the actual
position from the predetermined position is obtained by
simultaneously deflecting the beam in orthogonal directions.
27. The method according to claim 25 including:
writing a different predetermined pattern at different levels of
the wafer at different times through directing the beam over the
design area after each level of the wafer is formed;
and moving the beam in a predetermined path to each of a plurality
of predetermined positions within the design area in accordance
with the predetermined pattern at each of the levels while
dynamically electronically compensating at each of the
predetermined positions for the deviation of the actual position
within the actual area from the predetermined position due to the
actual area having a different location and shape relative to the
location and shape of the design area to cause the beam to be
shifted from the predetermined position and applied at the deviated
actual position so that a pattern is written within the actual area
in accordance with the predetermined pattern at each of the levels.
Description
In U.S. Pat. No. 3,644,700 to Kruppa et al, there is shown a method
and apparatus for controlling a square-shaped beam. The beam is
employed to both write desired patterns on chips of a semiconductor
wafer and to locate each chip relative to a predetermined position
through determining the positions of a pair of registration marks
for each chip by utilization of the beam. In the aforesaid Kruppa
et al patent, the location of the two registration marks insures
that the pattern can be written within the chip.
Because of the accuracy required in applying the beam to a field,
the size of each chip site must be limited to that of the writing
field so that any beam error therein is within a certain range.
Accordingly, the size of the writing fields cannot be enlarged to
enable a single pattern to be written within a single writing
field, which defines the maximum size of a chip site in the
aforesaid Kruppa et al patent, when the pattern size exceeds the
maximum field size within which the beam can be written and still
have the beam error within the desired range.
The present invention is an improvement of the method and apparatus
of the aforesaid Kruppa et al patent in that a single pattern can
be written in more than one writing field rather than being limited
to one writing field. Thus, the method and apparatus of the present
invention permit a semiconductor wafer to have continuous patterns
larger than the field to which the beam can be applied accurately
to be written therein.
The present invention accomplishes this through utilizing a
plurality of square or rectangular shaped fields with each field
overlying each of the adjacent fields. Thus, each field, which is
not on the periphery of the fields of the wafer, has an overlying
relation with four other adjacent fields. In each of the four
corners of the field, a registration mark is disposed in the
overlying area of the adjacent fields.
While it is desired for each of these registration marks to be at a
design position so that the registration marks would define a four
sided rectangular or square shaped field having the registration
marks at their corners, there is usually some slight deviation of
each of the registration marks from its design position since the
registration marks are written on the wafer within a certain
tolerance. Therefore, the registration marks are normally not at
their design positions but at some deviation therefrom. By
ascertaining the deviation of each of the four registration marks
for a particular field from the design locations for the
registration marks, the boundaries of the writing field are
located.
Since the beam is being applied in accordance with a predetermined
pattern in which the field was deemed to be a perfect square or
rectangle, these deviations of the registration marks for the
particular field result in the field not being a perfect square or
rectangle. Therefore, if the beam were to be applied in accordance
with the predetermined pattern, the beam may be applied beyond the
boundaries defined by the registration marks and into another field
if correction is not made.
While the patterns for writing within a specific field would be
such as to insure that the beam is not applied beyond the field
even with the deviations of the marks, this cannot be employed when
writing a single pattern in more than one field. This is because
the beam must be applied to each field separately because of the
required accuracy of the beam with respect to field size. Thus,
each line of the beam must stop at a specific boundary so that when
the beam is applied to the next adjacent field it will be applied
as a continuation of the prior location of the beam at the boundary
between the two adjacent field.
Accordingly, to insure that the beam is applied within the
boundaries of the field as defined by the actual locations of the
registration marks relative to the beam, it is necessary to
dynamically correct the position of the beam when it is stepped
from one predetermined position to the next within the field so
that the beam is applied to an actual position, which is a
deviation from the predetermined position, in accordance with the
actual site of the field as defined by the four registration marks
of the field. By this dynamic correction at each of the
predetermined positions, the beam writes the pattern within the
field boundaries as defined by the actual locations of the
registration marks.
When the fields are written by moving the beam from one field to
the next adjacent field in the X direction and to the right, the
registration marks in the upper and lower right hand corners of the
first field will be the registration marks in the upper and lower
left hand corners for the next field. Therefore, these two
registration marks define the common boundary between the two
fields and function as reference points to which the beam is
applied at the next of the adjacent fields. The other boundaries of
the field are similarly defined with respect to the registration
marks of the other adjacent fields.
It should be understood that reference points could be ascertained
relative to the actual locations of the registration marks and used
to define the boundaries of the field rather than the registration
marks per se. This shift would be accomplished within the computer,
but it would not have any effect on the concept of the pattern
being written within the field as defined by the four registration
marks at the corners of the field.
Through ascertaining the actual location of each of the
registration marks of a field, various digital constants can be
determined and applied throughout writing of the pattern within the
particular field. The digital constants are utilized to correct for
translation, magnification, rotation, and distortion of the beam in
the X and Y directions. By using the magnetic deflection voltages
for each of the X and Y directions at each of the predetermined
positions to which the beam is to be applied and then modifying
these voltages by the appropriate digital constants for the
particular field, correction voltages are applied for both the X
and Y directions to a set of electrostatic field plates to shift
the beam from the predetermined position to the actual deviated
position in accordance with the actual field as defined by the
actual location of the registration marks.
As a result of applying the correction voltage to shift the beam,
the beam is written within the boundaries of the field since the
beam would either be compressed or extended, for example, in each
line to compensate for the difference between the predetermined
position and the actual position.
The method and apparatus of the present invention is particularly
useful when it is desired to write a plurality of patterns at
different levels of a chip with each level being written at a
different time. Thus, the present invention enables overlay
accuracy between the written fields at various levels on a
chip.
The present invention accomplishes this through ascertaining the
actual location of each of the four registration marks of a field,
as previously mentioned, and retaining these actual locations for
reference throughout the various levels of pattern writing. If it
should be necessary to use a new set of registration marks, these
would be written with their actual locations determined with
respect to the actual locations of the prior registration marks,
which define the field. Thus, by using the digital constants to
correct the translation, magnification, rotation, and distortion of
the beam in the X and Y directions, the beam can always be shifted
from its predetermined position to its actual deviated position
irrespective of the level at which the pattern is being written to
insure that the pattern at each level has an accurate overlay with
the patterns at other levels of the field.
An object of this invention is to dynamically position a beam of
charged particles at each of the positions to which it is moved
within a field on a semiconductor wafer in accordance with the
boundaries of the field.
Another object of this invention is to provide a method and
apparatus for writing a continuous pattern with a beam of charged
particles in more than one field on a semiconductor wafer with each
field having a separate portion of the pattern written therein at
various times.
A further object of this invention is to dynamically position a
beam of charged particles at each of the positions to which it is
moved within an area on a target in accordance with the actual
boundaries of the area.
Still another object of this invention is to provide a method and
apparatus for writing a continuous pattern with a beam of charged
particles in more than one area of a target with each area having a
separate portion of the pattern written therein at different
times.
A still further object of this invention is to provide a method and
apparatus for automatically overlaying two separate patterns
written within an area on a target or within a field on a
semiconductor wafer with each pattern written therein at various
times.
The foregoing and other objects, features, and advantages of the
invention will be apparent from the following more particular
description of a preferred embodiment of the invention as
illustrated in the accompanying drawings.
In the drawings:
FIG. 1 is a schematic view showing an electron beam and the
apparatus for controlling the beam.
FIG. 2 is a schematic block diagram of a circuit arrangement for
dynamically supplying signals to shift the beam from each of its
predetermined positions to the actual deviated position in
accordance with the location of the registration marks of the field
to which the beam is being applied.
FIG. 3 is a schematic diagram showing the relation between an
actual field to which the beam is to be applied in conjunction with
the learn corrected field to which the beam would be applied
without dynamic correction for the location of the registration
marks.
FIG. 4 is a top plan view of a portion of a semiconductor wafer
having fields to which the beam is to be applied and showing the
relation of the overlapping fields.
FIG. 5 is an enlarged top plan view of a registration mark that
identifies one corner of a field within which an electron beam can
write.
FIG. 6 is a schematic wiring diagram showing the magnetic
deflection circuit for controlling the X magnetic deflection
coils.
FIG. 7 is a schematic wiring diagram showing the electrostatic
deflection circuit for controlling the X electrostatic deflection
plates.
Referring to the drawings and particularly FIG. 1, there is shown
an electron gun 10 for producing a beam 11 of charged particles in
the well-known manner. The electron beam 11 is passed through an
aperture 12 in a plate 14 to shape the beam 11. The beam 11 is
preferably square shaped and has a size equal to the minimum line
width of the pattern that is to be formed.
The beam 11 passes between a pair of blanking plates 16, which
determine when the beam 11 is applied to the material and when the
beam 11 is blanked. The blanking plates 16 are controlled by
circuits of an analog unit 17. The analog unit 17 is controlled by
a digital control unit 18 in the manner more particularly shown and
described in the copending patent application of Philip M. Ryan for
"Method And Apparatus For Controlling Movable Means Such As An
Electron Beam," Ser. No. 398,734, filed Sept. 19, 1973, and
assigned to the same assignee as the assignee of this application.
The digital control unit 18 is connected to a computer 19, which is
preferably an IBM 370 computer.
The beam 11 then passes through a circular aperture 21 in a plate
22. This controls the beam 11 so that only the charged particles
passing through the centers of the lenses (not shown) are used so
that a square-shaped spot without any distortion is produced.
The beam 11 is next directed through magnetic deflection coils 23,
24, 25, and 26. The magnetic deflection coils 23 and 24 control the
deflection of the beam 11 in a horizontal or X direction while the
magnetic deflection coils 25 and 26 control the deflection of the
beam 11 in a vertical or Y direction. Accordingly, the coils 23-26
cooperate to move the beam 11 in a horizontal scan by appropriately
deflecting the beam 11.
While the beam 11 could be moved in a substantially raster fashion
as shown and described in the aforesaid Kruppa et al patent, it is
preferably moved in a back and forth scan so that the beam 11 moves
in opposite directions along adjacent lines as shown and described
in the aforesaid Ryan application. Thus, the negative bucking
sawtooth of the type shown in FIG. 3b of the aforesaid Kruppa et al
patent is supplied to the coils 23 and 24 during forward scan while
a positive bucking sawtooth, which is of opposite polarity to the
sawtooth shown in FIG. 3b of the aforesaid Kruppa et al patent, is
supplied to the coils 23 and 24 during the backward scan.
The beam 11 then passes between a first set of electrostatic
deflection plates 27, 28, 29, and 30. The electrostatic deflection
plates 27 and 28 cooperate to deflect the beam in a horizontal or X
direction while the electrostatic deflection plates 29 and 30
cooperate to move the beam 11 in the vertical or Y direction. The
plates 27-30 are employed to provide any desired offset of the beam
11 at each of the predetermined positions or spots to which it is
moved. In the aforesaid Kruppa et al patent, the plates 27-30
corrected for linearity, but these correction signals are supplied
to the coils 23-26 in this application.
After passing between the electrostatic deflection plates 27-30,
the beam 11 then passes between a second set of electrostatic
deflection plates 31, 32, 33, and 34. The electrostatic deflection
plates 31 and 32 cooperate to deflect the beam 11 in the horizontal
or X direction while the electrostatic deflection plates 33 and 34
cooperate to deflect the beam 11 in the vertical or Y direction.
The plates 31 and 32 deflect the beam 11 in the X direction and the
plates 33 and 34 deflect the beam 11 in the Y direction from each
of the predetermined positions to which it is moved in accordance
with its predetermined pattern so that the beam 11 is applied to
its actual position based on the deviation of the area from its
designed position, both shape and location, in which the beam 11 is
to write.
The beam 11 is then applied to a target, which is supported on a
table 35. The table 35 is movable in the X and Y directions as more
particularly shown and described in the aforesaid Kruppa et al
patent.
The beam 11 is moved through A, B, and C cycles as shown and
described in the aforesaid Kruppa et al patent. The present
invention is concerned with supplying signals to shift the beam 11
from each of the predetermined positions to which it is stepped to
a deviated actual position, which is determined by the location of
an actual field in comparison with the design field, during the B
cycle when the pattern is being written.
As shown in FIG. 4, the target may comprise a plurality of fields
39 which overlap each other. A chip 40 may be formed within each of
the fields 39 so that there is a plurality of the chips 40 on a
semiconductor wafer 41 with each of the chips 40 having resist to
be exposed by the beam 11.
It should be understood that the chip 40 may comprise a plurality
of the fields 39 or one of the fields 39 may have a plurality of
the chips 40. The following description will be with one of the
chips 40 formed within each of the fields 39.
There is a registration mark 42 (schematically shown as a cross in
FIG. 4) at each of the four corners of each of the fields 39. As
shown in FIG. 4, the overlapping of the adjacent fields 39 results
in the same registration mark 42 being utilized for each of four
different adjacent fields 39. Thus, the registration mark 42 in the
lower right corner of the only complete field 39 shown in FIG. 4
also is the registration mark in the lower left corner for the
field 39 to the right of the complete field 39, the upper right
corner of the field below the complete field 39, and the upper left
corner of the field 39 which is diagonally to the right of the
completed field 39.
Each of the registration marks 42 is preferably formed of a
plurality of horizontally extending bars 43, preferably three in
number as shown in FIG. 5, and a plurality of vertically extending
bars 44, preferably equal in number to the number of the bars 43.
Any other suitable arrangement of registration marks can be
employed in which there can be scan of vertical edges of the mark
in the X direction and of horizontal edges of the mark in the Y
direction.
The overlapping of the fields 39 enables writing to occur between
the adjacent fields. The boundary of each of the chips 40 is within
the overlapping area of the field 39 of the chip 40 and is normally
defined by the lines extending between the registration marks
42.
As explained in the copending patent application of Ollie C.
Woodard for "Method And Apparatus For Detecting The Registration
Mark On A Target Such As A Semiconductor Wafer," Ser. No. 437,434,
filed Jan. 28, 1974, and assigned to the same assignee as the
assignee of this application, the exact location of each of the
registration marks 42 is obtained through passing the electron beam
11 over the vertical edges of the vertically disposed bars 44 of
the mark 42 during scans in the X direction and over the horizontal
edges of the horizontally disposed bars 43 of the mark 42 during
scans in the Y direction. Thus, as described in the aforesaid
Woodard application, the actual location of each of the
registration marks 42 is obtained.
If the registration marks 42 were located at their design
positions, then the design field, as defined by the registration
marks 42 being located at design positions 1, 2, 3, and 4 in FIG.
3, would exist, and the beam 11 would be applied thereto. The
design field 50 would be a perfect square or rectangle and is the
learn corrected field.
However, because of various factors such as the condition of the
surface of the wafer 41, the material of the wafer 41 at the
particular level, the tilt of the wafer 41, rotational error due to
location of the wafer 41, positional errors of the beam 11, and the
errors in putting down the registration marks 42, the registration
marks 42 are not located at the design positions 1, 2, 3, and 4 as
shown in FIG. 3. Instead, because of these various factors, the
registration marks 42 are located at positions such as positions
1', 2', 3', and 4', for example, as shown in FIG. 3. As a result,
an actual field 51, which is not necessarily a perfect square or
rectangle but is four sided, in which the beam 11 can write is
produced by the registration marks 42 being at the positions 1',
2', 3', and 4' rather than the design positions 1, 2, 3, and 4.
If it is desired to write the pattern in both the chip 40 within
the field 51 and the chip 40 within the field to the right of the
field 51, for example, then the line between the positions 2' and
3' must be accurately defined so that the beam 11 will form a
continuation of the same lines within the field 51 when writing in
the field to the right of the field 51. The line defined between
the positions 2' and 3' is the boundary between the chip 40 within
the field 51 and the chip 40 within the field to the right of the
field 51 so that this is a common boundary between the two chips
40. It should be understood that the area of the chip 40 within
which the beam 11 writes need not be the entire field as defined by
the positions of the registration marks 42 but can be smaller and
use the registration marks 42 as reference points.
The difference between the design and actual positions of each of
the registration marks 42 can be defined by setting forth the
difference between the design and actual positions of the mark 42
in both the X and Y directions. The equations for any specific mark
position are:
dX = A + BX + CY + DXY (1)
and
dY = E + FX + GY + HXY. (2)
In equations (1) and (2), X represents the design position of the
mark in the X direction and Y represents the design position in the
Y direction with dX being the distance between the design position
and the actual position in the X direction and dY being the
distance between the actual position and the design position in the
Y direction. Each of A, B, C, D, E, F, G, and H is a digital
constant which can be ascertained for the particular field within
which the beam 11 is to be applied.
The digital constant A represents the translation of the beam in
the X direction while the digital constant E represents the
translation of the beam 11 in the Y direction. The digital constant
B represents the magnification error in the X direction, and the
digital constant G represents the magnification error in the Y
direction. The digital constant C represents the rotation error of
the beam 11 in the X direction, and the digital constant F
represents the rotation error of the beam 11 in the Y direction.
The digital constant D represents the distortion of the beam 11 in
the X direction, and the digital constant H represents the
distortion of the beam 11 in the Y direction.
Thus, to determine the distance between the four positions 1, 2, 3,
and 4 of the design registration marks for the design field 50 and
the four positions 1', 2', 3', and 4' for the actual registration
marks defining the actual field 51, the following equations would
be employed for determining the distances in the X direction with
each subscript corresponding to the particular position 1, 2, 3,
and 4:
dX.sub.1 = A + BX.sub.1 + CY.sub.1 + DX.sub.1 Y.sub.1 (3)
dX.sub.2 = A + BX.sub.2 + CY.sub.2 + DX.sub.2 Y.sub.2 (4)
dX.sub.3 = A + BX.sub.3 + CY.sub.3 + DX.sub.3 Y.sub.3 (5)
and
dX.sub.4 = A + BX.sub.4 + CY.sub.4 + DX.sub.4 Y.sub.4. (6)
Similarly, each of the distances between the actual positions 1',
2', 3', and 4' of the registration marks 42 with respect to the
design positions 1, 2, 3, and 4, respectively, in the Y direction
with the subscripts corresponding to the four positions 1, 2, 3,
and 4 are defined by the following equations:
dY.sub.1 = E + FX.sub.1 + GY.sub.1 + HX.sub.1 Y.sub.1 (7)
dY.sub.2 = E + FX.sub.2 + GY.sub.2 + HX.sub.2 Y.sub.2 (8)
dY.sub.3 = E + FX.sub.3 + GY.sub.3 + HX.sub.3 Y.sub.3 (9)
and
dY.sub.4 = E + FX.sub.4 + GY.sub.4 + HX.sub.4 Y.sub.4. (10)
As an example, the design field 50 is shown as being a square. With
this example, the distance between the marks 42 at positions 1 and
2 in the design field 50 or positions 3 and 4 in the field 50 is
the same and may be defined by W. Similarly, the height of the
field 50 between the positions 1 and 4 or positions 2 and 3 is the
same and may be defined as h.
With this special case of symmetry between the four positions 1, 2,
3, and 4 and X being positive to the right and Y being positive
downwardly in FIG. 3, then the X and Y locations of each of the
four positions can be determined relative to h and W. These are:
##EQU1## With these values substituted in equations (3) to (6) for
dX.sub.1 to dX.sub.4 and equations (7) to (10) for dY.sub.1 to
dY.sub.4 and solving for the digital constants A to H, the
following equations result: ##EQU2##
Accordingly, since the distance of each of the actual positions 1',
2', 3', and 4' from the design positions 1, 2, 3, and 4,
respectively, in each of the X and Y directions can be ascertained
with the method and apparatus shown and described in the aforesaid
Woodard application, the digital constants A through H for the
field 51, as defined by the positions 1', 2', 3', and 4' of the
registration marks 42, can be calculated in the computer 19.
Although equations (11) to (18) are for the special case of
symmetry between the four mark positions, similar equations could
be generated for the general case of non-symmetry between the four
positions 1, 2, 3, and 4 of the design registration marks 42 so
that dX.sub.1, dX.sub.2, dX.sub.3, dX.sub.4, dY.sub.1, dY.sub.2,
dY.sub.3, and dY.sub.4 can be obtained. Thus, equations (3) to (6)
could be written as ##EQU3## and equations (7) to (10) could be
written as ##EQU4## where each of the single column matrices in
each of equations (19) and (20) is a vector matrix and the four
column matrix in each of equations (19) and (20) is the system
matrix.
By transposing the four column matrix, equation (19) can be written
as ##EQU5## and replace equations (11) to (14). Similarly, by
transposing the four column matrix, equation (20) can be written as
##EQU6## and replace equations (15) to (18). In each of equations
(21) and (22), the four column matrix is the inverse matrix of the
system matrix and is calculated by the computer 19.
From equation (21), A, B, C, and D can be obtained. From equation
(22), E, F, G, and H can be obtained.
The digital constants A, B, C, D, E, F, G, and H are ascertained
through using the design locations of the positions 1, 2, 3, and 4
in the X and Y directions, which are known for the design field 50,
along with the actual distances, as defined by dX.sub.1 to dX.sub.4
and dY.sub.1 to dY.sub.4, between the positions 1, 2, 3, and 4 and
the positions 1', 2', 3', and 4', respectively, in the X and Y
directions. Each of the positions of the beam 11 in the field 50
also is defined by the magnetic deflection voltage of the beam 11
at the particular position.
Thus, after the digital constants A, B, C, D, E, F, G, and H for
the actual field 51 have been solved, the magnetic voltages for X
and Y can be substituted in equation (1) for dX and equation (2)
for dY to ascertain the deflection voltage that must be applied to
the beam 11 when it is at any predetermined position (X, Y) such as
position 5, for example, to shift the beam 11 to its corresponding
actual position (X', Y') such as position 5', for example. Thus, dX
is the deflection voltage to be applied for the X direction to
shift the beam 11 from its predetermined position X to its actual
position X', and dY is the deflection voltage to be applied to
shift the beam 11 in the Y direction from its predetermined
position Y to its actual position Y'.
Accordingly, with the magnetic deflection voltage at each of the
predetermined positions to which the beam 11 is stepped during the
writing of the pattern being different, the substitution of the X
and Y magnetic deflection voltages in equations (1) and (2) enables
determination of dX and dY for any position in the writing pattern.
This enables the corrections to be correlated to the magnetic
deflection voltages.
The voltage, which is obtained by solving equation (1) for dX, is
the deflection voltage applied to the electrostatic deflection
plates 31 and 32, and the deflection voltage, which is obtained by
solving equation (2) for dY, is supplied to the electrostatic
deflection plates 33 and 34. Thus, the deflection voltages at each
of the predetermined positions causes a shift of the beam 11 to
dynamically correct the deflection of the beam 11 at each of the
predetermined positions to which it is stepped so that the beam 11
is moved to the actual deviated position whereby the predetermined
pattern is written within the actual field 51 rather than the
design field 50 for which the pattern was programmed in the
computer 19.
Therefore, to write the predetermined pattern within the actual
field 51 rather than the design field 50, it is necessary to
continuously determine the X and Y magnetic deflection voltages at
any position in the field. After determining the appropriate
correction voltages (dX and dY) with the X and Y magnetic
deflection voltages substituted in equations (1) and (2), the
correction voltage (dX) is supplied to the electrostatic deflection
plates 31 and 32 for the X direction and the correction voltage dY
is supplied to the electrostatic deflection plates 33 and 34 for
the Y direction.
Accordingly, to continuously apply the correction to the beam 11,
the circuit of FIG. 2 is employed. This enables dynamic correction
of the beam 11 as it is stepped to each of the predetermined
positions in accordance with the pattern to be written so that the
beam 11 is not applied to the predetermined position to which it is
stepped by the magnetic coils 23-26 but is shifted to the actual
deviated position. As shown and described in the aforesaid Ryan
application, it should be understood that the beam 11 can be on or
off for the entire time that it is at a position or on for only a
portion of the time.
As shown in FIG. 2, the X deflection voltage is supplied from the
analog unit 17 through a line 55 while the Y deflection voltage is
supplied from the analog unit 17 through a line 56. The X
deflection voltage on the line 55 is correlated to the deflection
current applied to the magnetic deflection coils 23 and 24 for the
X direction at the predetermined position, and the Y deflection
voltage on the line 56 is correlated to the deflection current
applied to the magnetic deflection coils 25 and 26 for the Y
direction at the predetermined position. The lines 55 and 56 are
connected to an analog multiplier 57, which has the product of the
X and Y deflection voltages as its output and supplied to each of a
pair of multiplying digital to analog converters (MDAC) 58 and
59.
In addition to the input from the analog multiplier 57, the
multiplying digital to analog converter 58 also has an input from
the digital control unit 18 with this input being the digital
constant D as defined by an eight bit word supplied from the
digital control unit 18 to the multiplying digital to analog
converter 58. The output of the multiplying digital to analog
converter 58 is DXY, which corrects for distortion and trapezoidal
errors in the X direction and is supplied as one of the inputs to
an operational amplifier 60. The operational amplifier 60 is a
summing amplifier for all of its four inputs.
In addition to the input from the analog multiplier 57, the
multiplying digital to analog converter 59 also has an input from
the digital control unit 18. This input is the digital constant H
and is defined by an eight bit word from the digital control unit
18. The output of the multiplying digital to analog converter 59 is
the product of its inputs of H and XY. The output of HXY, which
corrects for distortion and trapezoidal error in the Y direction,
is supplied as one of the four inputs to an operational amplifier
61 in which all of its four inputs are summed.
The other inputs to the amplifier 60 are from a digital to analog
converter (DAC) 62, and multiplying digital to analog converters
(MDAC) 63 and 64. Similarly, the other inputs to the amplifier 61
are from a digital to analog converter (DAC) 65 and multiplying
digital to analog converters (MDAC) 66 and 67.
The input to the digital to analog converter 62 is the digital
constant A. This input is a 10 bit word from the digital control
unit 18. Thus, the output of the digital to analog converter 62 to
the amplifier 60 is A, which corrects for translation in the X
direction.
The multiplying digital to analog converter 63 has a first input of
the X deflection voltage from the line 55. A second input to the
multiplying digital to analog converter 63 is the digital constant
B, which is supplied from the digital control unit 18 as an eight
bit word. The output of the multiplying digital to analog converter
63 to the amplifier 60 is the product of the two inputs so that its
output is BX, which corrects for magnification in the X
direction.
The multiplying digital to analog converter 64 has a first input of
the Y deflection voltage from the line 56. The multiplying digital
to analog converter 64 has the digital constant C as its second
input, which is supplied as a ten bit word from the digital control
unit 18 to the multiplying digital to analog converter 64.
Accordingly, the output of the multiplying digital to analog
converter 64 to the amplifier 60 is CY, which corrects for rotation
in the X direction.
Accordingly, the four inputs, which are summed by the amplifier 60
to which they are supplied, comprise A, BX, CY, and DXY. These
inputs are what define dX in equation (1) so that the output of the
amplifier 60 is the deflection voltage required to be supplied to
the electrostatic deflection plates 31 and 32 to shift the beam 11
from its predetermined position to the actual deviated position in
the X direction. The output of the summing amplifier 60 is
amplified by an amplifier 68 prior to being supplied to the
electrostatic deflection plates 31 and 32 as a balanced
differential signal.
The digital to analog converter 65 has only the digital constant E
as its input, which is supplied from the digital control unit 18 as
a ten bit word. Thus, the output of the digital to analog converter
65 to the summing amplifier 61 is E, which corrects for translation
in the Y direction.
The multiplying digital to analog converter 66 has a first input of
the X deflection voltage from the line 55. The other input to the
multiplying digital to analog converter 66 is the digital constant
F, which is supplied from the digital control unit 18 as a 10 bit
word. The output of the multiplying digital to analog converter 66
to the amplifier 61 is the product of its inputs so that its output
is FX, which corrects for rotation in the Y direction.
The multiplying digital to analog converter 67 has a first input of
the Y deflection voltage from the line 56. The multiplying digital
to analog converter 67 has the digital constant G as its second
input, which is supplied from the digital control unit 18 as an
eight bit word. The output of the multiplying digital to analog
converter 67 to the amplifier 61 is GY, which is the product of its
inputs and corrects for magnification in the Y direction.
Accordingly, the inputs to the amplifier 61 are E, FX, GY, and HXY.
When added, these inputs produce dY, which is the output from the
summing amplifier 61. This output is supplied from the summing
amplifier 61 through an amplifier 69 to the electrostatic
deflection plates 33 and 34 to shift the beam 11 in the Y direction
from its predetermined position to the actual position.
Since the X and Y deflection voltages on the lines 55 and 56 are
continuously changing as the beam 11 is stepped from one
predetermined position to another, there is a continuous correction
of the signals to the electrostatic deflection plates 31-34.
Accordingly, the beam 11 is applied to the actual deviated position
rather than the predetermined position as it is stepped from one
position to another in accordance with its predetermined pattern,
which it is writing within the chip 40 located within the
boundaries of the actual field 51.
Because of the shifting of the beam 11 as it writes within the
actual field 51, a single, continuous pattern can be written in
more than one field. This is because the pattern being written
within the actual field 51 can be written up to the boundary. Then,
when the beam is to be applied to the next adjacent field, it is
again applied to the actual field through using the circuit of FIG.
2. Of course, the digital constants A, B, C, D, E, F, G, and H will
be different than they were for the previous field. However, they
will be the same throughout the field for which they were
determined. Of course, in this arrangement, the chip 40 would
comprise all of the fields in which the single pattern is
written.
Accordingly, once the wafer 41 has been disposed beneath the beam
11 and the beam 11 determines the location of the registration
marks 42 for the initial field, then the patterns can be written
continuously throughout the remainder of the wafer 41 without any
mechanical corrections with respect to the actual location of each
of the fields as all corrections will be made through the circuit
of FIG. 2. Of course, the location of the registration marks 42 for
each of the actual fields 51 must be made before any writing of the
pattern in this field occurs.
It should be understood that the beam 11 attempts to locate the
registration marks 42 at the design positions, but these do not
occur because of the various factors previously mentioned.
It should be understood that the beam 11 requires the use of a
focus grid and a calibration grid in the same manner as described
in the aforesaid Kruppa et al patent. One suitable example of these
grids is the focus and calibration grids of the aforesaid Kruppa et
al patent.
While each of the registration marks 42 has been described as
having the bars 43 and 44 formed as depressions, it should be
understood that the bars 43 and 44 could be formed otherwise as
long as they produced a signal when the beam 11 passed thereover.
For example, each of the bars 43 and 44 could be a raised
portion.
As previously mentioned, the magnetic deflection coils 23-26
cooperate to move the beam in a horizontal or X scan by
appropriately deflecting the beam 11. The circuit for controlling
the X magnetic deflection coils 23 and 24 is shown in FIG. 6.
This circuit includes both positive constant current sources 70,
71, and 72 and negative constant current sources 73, 74, and 75.
The constant current sources 70-75, controlled by logic control
signals from the digital control unit 18 and derived from an X
counter, which is part of the digital control unit 18, charge a
capacitor 77.
Each of the positive and negative constant current sources is not
the same value so that the charge of the capacitor 77 may be
different depending on which of the current sources 70-75 is used.
Thus, the charge for the capacitor 77 for the different constant
current sources 70-75 produces different voltage ramps, which have
slopes depending upon the value of the turned on current source.
The length of the ramp is dependent upon the time that the current
source is activated. It should be understood that more than one of
the current sources 70-75 can be turned on simultaneously to
produce a variety of slopes.
The positive current source 70 is turned on by a signal on a line
78 from the digital control unit 18 in accordance with the X
counter only during the B cycle. The positive current source 71 is
turned on by a signal on a line 79 from the digital control unit 18
in accordance with the X counter only during the A cycle.
The negative constant current source 74 is also turned on only
during the A cycle by a signal on a line 80 from the digital
control unit 18 in accordance with the X counter. The negative
constant current source 73 is turned on by a signal on a line 81
from the digital control unit 18 in accordance with the X counter
only during the B cycle.
The digital control unit 18, in accordance with the X counter, may
turn on the positive current source 72 by a signal on a line 82 or
the negative current source 75 by a signal on a line 83. Only one
of the current sources 72 and 75 is turned on at one time.
The current sources 72 and 75 are used primarily during the C cycle
to move the beam left or right as required for focusing. They may
be used at other times to probe the beam movement as desired.
The positive constant current source 70 is used to move the beam 11
in the X scans in one direction. The negative current source 73 is
used to move the beam 11 in the X scans in the other direction.
The capacitor 77 is connected to the magnetic deflection coils 23
and 24 through an operational amplifier 84, corrector circuitry 85,
a summing point 86, and a driver amplifier 87. The driver amplifier
87 and the summing point 86 function as a summing amplifier. The
amplifier 84 forms an integrator along with the capacitor 77 and
isolates the current sources 70-75 from the driver amplifier 87,
which converts the voltage to current, and from the corrector
circuitry 85.
The corrector circuitry 85 compensates for non-linearity of the
beam 11 to a degree. Thus, the corrector circuitry 85 modifies the
voltage ramps so that the beam deflection approaches linearity.
The remainder of the correction for non-linearity of the beam 11 is
made through a ten bit digital to analog converter (DAC) 88, which
is connected to an amplifier 89. One suitable example of the 10 bit
digital to analog converter 88 is sold as model No. DAC-HI 10B by
Datel Systems Inc.
The 10 bit digital to analog converter 88 is connected to the
digital control unit 18 to receive correction words therefrom, and
its output is supplied to the negative input of the amplifier 89
through a resistor 90. A capacitor 91 cooperates with the resistor
90 to integrate the output of the 10 bit digital to analog
converter 88. The output of the amplifier 89 is supplied as one of
the inputs to the summing point 86 to complete the correction for
non-linearity.
The digital control unit 18 is connected through a line 92 and a
diode 93 to an FET 94. The diode 93 and the FET 94 together form an
analog switch. When a retrace gate signal is supplied from the
digital control unit 18 in accordance with the X counter to the
line 92, the FET 94 is turned on to cause a reset of the correction
for non-linearity from the output of the amplifier 89 since the
beam 11 moves in the opposite direction after the retrace gate.
During retrace time, the voltage developed across a sense resistor
94' by the current returning from the deflection coils 23 and 24 is
fed to a comparing amplifier 95 and compared with a reference
signal supplied from a 16 bit digital to analog converter (DAC) 96,
which is controlled by a 16 bit word from the digital control unit
18, through a line 97.
The comparing amplifier 95 amplifies the difference between the
voltage across the sense resistor 94' and the reference voltage and
supplies it as an error voltage to an analog switch 98. During
retrace time, a signal through a line 99 from the digital control
unit 18 in accordance with the X counter closes the analog switch
98 causing the error voltage to supply current to the integrator,
which comprises the capacitor 77 and the amplifier 84, through a
resistor 100. This charges the capacitor 77 in the proper direction
to cause the deflection voltage across the sense resistor 94' to
approach the reference voltage. Current is supplied until the error
voltage is reduced to zero at which time the deflection voltage is
equal to the reference voltage. This insures that the beam 11 is
ready for scanning in the opposite X direction. It should be
understood that the signal on the line 99 is removed at the end of
retrace time.
By properly selecting the values of the positive constant current
sources 70, 71, and 72 and the negative constant current sources
73, 74, and 75, the speed at which the beam 11 scans in each of the
X directions during the various cycles is controlled. If the
positive constant current source 70 is considered to be +I and the
negative constant current source 73 is considered to be -I, then
the source 71 is + 1/10 I, the source 72 is + 1/660 I, the source
74 is - 1/10 I, and the source 75 is - 1/660 I.
As shown in FIG. 6, the line 55, which is connected to the analog
multiplier 57 in FIG. 2, is connected between the coil 24 and the
sense resistor 94'. This enables the deflection voltage to be
obtained as the beam 11 moves in the X direction.
A similar type of magnetic deflection circuit is utilized with the
Y deflection coils 25 and 26. This will not be described in
detail.
Referring to FIG. 7, there is shown an electrostatic deflection
circuit for controlling the X electrostatic deflection plates 27
and 28. The Y electrostatic deflection plates 29 and 30 would be
controlled by a similar type of circuit.
The electrostatic circuit has an input from the digital control
unit 18 in accordance with the X counter through a line 110 to a
clamping NPN transistor 111, which resets the charge on a capacitor
112. The capacitor 112 is connected to a positive constant current
source 113. The capacitor 112 and the constant current source 113
produce a positive bucking sawtooth as an output.
The capacitor 112 is connected through a high impedance amplifier
114 to a summing point 115. The summing point 115 is connected to a
push-pull amplifier 116, which is connected to the X electrostatic
deflection plates 27 and 28. The push-pull amplifier 116 inverts
the signal from the amplifier 114 so that the signal, which is
produced by the amplifier 114, is a negative sawtooth at the output
of the push-pull amplifier 116. Thus, this steps the beam 11 from
left to right as discussed in the aforesaid Kruppa et al
patent.
A second circuit produces a positive bucking sawtooth at the output
of the push-pull amplifier 116 to cause the beam 11 to step from
right to left in the X direction. This circuit includes an input
from the digital control unit 18 in accordance with the X counter
through a line 120 to a clamping PNP transistor 121, which resets
the charge on a capacitor 122. The capacitor 122 is connected to a
negative constant current source 123. The capacitor 122 and the
constant current source 123 produce a negative sawtooth as an
output.
The capacitor 122 is connected through a high impedance amplifier
124 to the summing point 115 from which the negative sawtooth is
supplied to the push-pull amplifier 116, which inverts the input to
produce a positive bucking sawtooth as its output. It should be
understood that the amplifiers 114 and 124 isolate the capacitors
112 and 122, respectively, from the push-pull amplifier 116.
The electrostatic deflection circuit also is utilized to produce
offset of the beam in the X direction in either the direction in
which the beam 11 is moving or the opposite direction. The offset
signal is supplied to the summing point 115 from a four bit digital
to analog converter 125, which receives its input from the digital
control unit 18 (see FIG. 1) in the manner more particularly shown
and described in the aforesaid Ryan application.
When the beam 11 is being calibrated in the B cycle during the
calibration operation in the manner more particularly shown and
described in the aforesaid Kruppa et al patent to determine the
deflection of the beam 11 in the vertical or Y direction, the line
110 or the line 120 receives a signal to cause the bucking sawtooth
to be applied for a period of four lines to the push-pull amplifier
116. This bucking sawtooth is supplied due to signals from the
digital control unit 18 on the line 110 or 120. During writing, the
line 110 or 120 is activated by the digital control unit 18 in
accordance with the X counter such that the negative and positive
bucking sawtooths are operative for a period of every other line of
scan in accordance with the direction in which the beam 11 is
moving.
While the present invention has been described with respect to only
a single level in which patterns are written, it should be
understood that it has particular utility in the writing of
patterns at different levels and at separate times for the same
field location. With the present invention, accurate overlay of the
pattern at each of the different levels is obtained with respect to
the patterns at the other levels which are written at various
separate times.
While the present invention has been described as exposing a
resist, it should be understood that exposure may be made of any
other phenomenon. For example, there could be exposure of silicon
dioxide that is to have its etch rating enhanced.
While the present invention has described the apparatus as being
employed to expose the resist on the chips of a semi-conductor
wafer, it should be understood that the present invention may be
employed anywhere it is desired to correct or change the position
of a beam, which moves in any deflection fashion, without affecting
the history of the beam in its deflection movement. Thus, for
example, the present invention could be readily employed to produce
engineer drawings on a cathode-ray tube or to control an electron
beam welder or cutter.
While the present invention has described the detection of the
electrons as being by PIN diodes, it should be understood that any
suitable electron detector could be used. For example, a
scintilator-photomultiplier or a direct electron multiplier could
be employed.
While the target has been described as being a semiconductor wafer,
for example, it should be understood that the target could be other
materials. For example, the target could be a material in which a
mask could be formed by the beam, for example.
While the beam has been described as being moved in a line by line
scan, it should be understood that such is not a requisite for
satisfactory operation. Thus, the beam can be moved in any fashion
from one position to another within the field in which the pattern
is written. For example, the beam could be continuously moved with
continous dynamic correction occurring.
An advantage of this invention is that a single pattern can be
written in more than one field. Another advantage of this invention
is that it improves overlay accuracy. A further advantage of this
invention is that it eliminates the need for mechanical correction
for variations due to placing the wafer under the beam.
While the invention has been particularly shown and described with
reference to a preferred embodiment thereof, it will be understood
by those skilled in the art that the foregoing and other changes in
form and details may be made therein without departing from the
spirit and scope of the invention.
* * * * *