Mask and charged particle beam exposure method using the mask

A transmission mask is used when exposing patterns by a charged particle beam which passes therethrough. The transmission mask includes a plate, and a plurality of rectangular blocks formed on a surface of the plate and having an area approximately equal to a cross sectional area of the charged particle beam irradiated thereon, where the blocks include a first block in which at least one transmission hole is provided and a second block in which no transmission hole is provided. The transmission of the first block is partly irradiated by the charged particle beam when varying the size of the exposing pattern. A single second block is provided immediately adjacent to at least two first blocks, so that an irradiating position of the charged particle beam can be varied with respect to both the two first blocks from the single second block.

BACKGROUND OF THE INVENTION 
The present invention generally relates to masks and charged particle beam 
exposure methods using the masks, and more particularly to a mask having 
transmission hole which is partially irradiated by a charged particle beam 
when exposing variable patterns corresponding to elements of a circuit 
pattern of an integrated circuit, and to a charged particle beam exposure 
method which uses such a mask for the charged particle beam exposure. 
The photolithography technique was popularly used to form fine patterns. 
But as the integration density of integrated circuit increased, charged 
particle beam exposure methods using an electron beam, an ion beam and the 
like or, an exposure method using an X-ray have been developed to form 
even finer patterns. 
According to the electron beam exposure method which uses the electron 
beam, it is possible to form fine patterns of 1 .mu.m or less because the 
spot of the electron beam can be reduced to several .ANG.. However, 
because the electron beam exposure method draws the pattern, the spot of 
the electron beam must be reduced as the pattern size is reduced, and the 
exposure time becomes considerably long. The block exposure method was 
developed to overcome this problem of long exposure time. 
The block exposure method uses a mask having a plurality of grouped 
regions, and each grouped region includes a plurality of blocks. Each 
block includes a plurality of holes which correspond to the patterns which 
frequently appear in the circuit pattern such as the integrated circuit 
(IC). The charged particle beam is irradiated on a selected one of the 
blocks. 
FIG. 1 shows an essential part of an example of a conventional exposure 
apparatus for carrying out the conventional block exposure method. An 
electron beam output from an electron gun 1 is formed into a beam B1 
having a rectangular cross section as it passes through a rectangular 
transmission hole 2. The beam B1 is deflected towards a specified 
transmission hole of a transmission mask 4 by deflection electrodes 3. The 
transmission mask 4 includes a plate with a plurality of grouped regions 
4a as shown in FIG. 2A, and each grouped region 4a is made up of a 
plurality of blocks 4b. 
As shown in FIG. 2B, each block 4b within the grouped region 4a of the 
plate includes a plurality of transmission holes 5 having shapes 
corresponding to elements which form the circuit pattern such as the IC. 
The block 4b may include only one transmission hole corresponding to a 
single pattern which is used for exposing variable shapes or, transmission 
holes corresponding to alignment patterns. Each block 4b is exposed during 
one exposure by the beam B1. 
The deflection electrodes 3 electrostatically deflect the beam B1 to expose 
one selected block 4b within one grouped region 4a. But when selecting 
other blocks 4b within other grouped regions 4a, the transmission mask 4 
must be moved mechanically by mask moving means Ax and Ay. The mask moving 
means Ax moves the transmission mask 4 in the direction of the X-axis, and 
the mask moving means Ay moves the transmission mask 4 in the direction of 
the Y-axis. 
A beam B2 which is formed by passing the beam B1 through the transmission 
hole 5 of the selected block 4b is projected on a wafer 8 via a reduction 
lens 6 and an objective lens 7. The beam B2 is projected onto a 
predetermined position on the wafer 8 by an electrostatic deflector 9 and 
an electromagnetic deflector 10. 
In order to effectively reduce the number of exposures and improve the 
throughput using this block exposure method, it is conceivable to make the 
area of the block 4b which becomes the exposure repeating unit as large as 
possible. But in this case, it also becomes necessary to increase the 
cross section of the electron beam. If the cross section of the electron 
beam is increased, the charge density of the electron beam decreases, and 
it becomes necessary to increase the irradiation time of each beam 
exposure. As a result, there is a limit to improving the throughput by 
increasing the area of the block 4b. 
On the other hand, it is also conceivable to increase the area of the 
transmission mask 4 itself, so as to increase the number of blocks 4b 
which can be arranged on the transmission mask 4. But in this case, the 
number of times the transmission mask 4 must be moved mechanically by the 
mask moving means Ax and Ay increases. As a result, the throughput does 
not improve notably, and in addition, it becomes necessary to improve the 
function of deflecting the electron beam. 
In view of the above, an improved exposure method was previously proposed 
in a U.S. Pat. No. 5,036,209. This proposed method uses the transmission 
mask 4 having the blocks 4b grouped within the respective grouped regions 
4a as shown in FIG. 2A. In addition, the grouped regions 4a and the blocks 
4b within each grouped region 4a are respectively arranged so that the 
holes 5 and the blocks 4b which are time-sequentially used for the 
exposure are located close to each other and in such a manner that the 
time required to move the transmission mask 4 mechanically and the time 
required to deflect the electron beam are minimized. 
However, this proposed method is effective only when repeatedly drawing 
basic patterns. This proposed method is not effective when drawing 
non-repeating patterns by passing the beam B1 having the rectangular cross 
section through a part of the transmission hole in the transmission mask 4 
for forming variable shapes, as will be described hereinafter. 
FIGS. 3A through 3D are diagrams for explaining a method of exposing a 
desired pattern corresponding to the circuit pattern of the IC, by 
irradiating the beam B1 having the rectangular cross section over a 
transmission hole 11 which is used to form variable shapes. The shape of 
the exposed pattern is varied by controlling the irradiating position of 
the beam B1 relative to the transmission hole 11. For example, a 
triangular hole formed in one block 4b is used as the transmission hole 
11. The cross section of the beam B1 is varied depending on the overlap of 
the beam B1 and the transmission hole 11. 
In the case shown in FIG. 3A where the beam B1 overlaps a part of the 
triangular transmission hole 11, a shaped beam B2 having a small 
triangular cross section is obtained as shown in FIG. 3B. On the other 
hand, if the beam B1 overlaps the entire triangular transmission hole 11 
as shown in FIG. 3C, a shaped beam B2 having a large triangular cross 
section is obtained as shown in FIG. 3D. However, in the case shown in 
FIG. 3A, the beam B1 overlaps both the block 4b1 in which the transmission 
hole 11 is provided and the block 4b2 which is adjacent to the block 4b1. 
For this reason, no transmission hole can be provided within the adjacent 
block 4b2 so as to prevent an unwanted pattern from being formed when the 
beam B1 overlaps the two mutually adjacent blocks 4b1 and 4b2. 
Therefore, with respect to one transmission hole 11 within one block 4b 
which is used to form variable shapes, it becomes necessary to provide at 
least one adjacent block 4b in which no transmission hole is provided. In 
addition, depending on the shape of the transmission hole 11 which is used 
to form the variable shapes and depending on the kind of overlap of the 
beam B1 relative to the transmission hole 11, it may be necessary to 
provide more than one block 4b in which no transmission hole may be 
provided with respect to one block 4b in which the transmission hole 11 
for forming the variable shape is provided. In other words, the number of 
blocks 4b in which no transmission hole may be provided, that is, wasted 
area, increases. As a result, there is a problem in that the efficiency 
with which the transmission holes are arranged in the transmission mask 4 
deteriorates. Furthermore, if the efficiency with which the transmission 
holes are arranged in the transmission mask 4 deteriorates, there are also 
problems in that the time required to move the transmission mask 4 
mechanically and the time required to deflect the electron beam increase. 
SUMMARY OF THE INVENTION 
Accordingly, it is a general object of the present invention to provide a 
novel and useful mask and a charged particle beam exposure method using 
the mask, in which the problems described above are eliminated. 
Another and more specific object of the present invention is to provide a 
transmission mask adapted for use in exposing patterns by a charged 
particle beam which passes therethrough, comprising a plate, and a 
plurality of rectangular blocks formed on a surface of the plate and 
having an area approximately equal to a cross sectional area of the 
charged particle beam irradiated thereon, where the blocks include a first 
block in which at least one transmission hole is provided and a second 
block in which no transmission hole is provided, the transmission hole of 
the first block is partly irradiated by the charged particle beam when 
varying the size of the exposing pattern, and a single second block is 
provided immediately adjacent to at least two first blocks, so that an 
irradiating position of the charged particle beam can be varied with 
respect to both the two first blocks from the single second block. 
According to the transmission mask of the present invention, it is 
possible to minimize the area in which the provision of the transmission 
hole is prohibited, and improve the efficiency with which the transmission 
holes are arranged on the transmission mask. In addition, it is 
unnecessary to provide one second block for each first block. 
Still another object of the present invention is to provide a charged 
particle beam exposure method which exposes patterns on an exposing 
surface using a transmission mask which includes a plurality of blocks 
including a first block in which at least one transmission hole is 
provided and a second block in which no transmission hole is provided, 
where the charged particle beam exposure method comprises the steps of (a) 
shaping a charged particle beam into a first beam having a rectangular 
cross section by a shaping means, (b) arranging the transmission mask 
between the shaping means and the exposing surface so that the rectangular 
cross section of the first beam irradiated on the transmission mask is 
approximately equal to an area of one block, (c) irradiating the first 
beam on the transmission mask with an overlap between two predetermined 
first and second blocks which are immediately adjacent to each other to 
partly irradiate a transmission hole of the predetermined first block by 
the first beam when varying the size of the exposing pattern, where the 
predetermined second block is provided immediately adjacent to at least 
two first blocks including the predetermined first block, so that an 
irradiating position of the first beam can be varied with respect to both 
the two first blocks from the predetermined second block, and (d) 
irradiating the exposing surface by a second beam which is shaped when the 
first beam passes through the transmission mask. According to the charged 
particle beam exposure method of the present invention, it is possible to 
reduce the number of times and the distance the transmission mask must be 
moved during the exposure. As a result, the exposure time as a whole can 
be reduced, thereby enabling an efficient charged particle beam exposure. 
Other objects and further features of the present invention will be 
apparent from the following detailed description when read in conjunction 
with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
First, a description will be given of the operating principle of the 
present invention, by referring to FIG. 4. A transmission mask used in the 
present invention has a plurality of blocks 4b respectively including a 
transmission hole 11 for forming a variable shape corresponding to the 
element of the circuit pattern of the IC. This transmission mask is 
arranged between the rectangular transmission hole 2 which is used to form 
a charged particle beam having a rectangular cross section (hereinafter 
simply referred to as a rectangular beam B1) and an exposing surface which 
corresponds to the surface of the wafer 8 shown in FIG. 1, and the 
irradiating position of the rectangular beam B1 is controlled relative to 
the selected transmission hole 11 so as to form a desired shaped beam B2. 
The shaped beam B2 is the charged particle beam which is obtained after 
passing the rectangular beam B1 through the transmission hole 11. 
The present invention defines the positional relationship of the 
transmission hole 11 and a prohibited block 4i in which the arrangement of 
the transmission hole is prohibited. In other words, when moving the 
rectangular beam B1 in X-Y directions on an X-Y plane so as to vary the 
irradiating position of the rectangular beam B1 relative to the 
transmission hole 11, a moving direction in which the cross sectional area 
of the shaped beam B2 gradually increases will be defined as a "gradually 
increasing direction". The transmission hole 11 is always arranged 
relative to the prohibited block 4i so that the transmission hole 11 is 
located on the gradually increasing side relative to the prohibited block 
4i. 
Accordingly, a transmission hole 11 having the +Y direction as its 
gradually increasing direction is arranged on the +Y direction side of a 
prohibited block 4i as shown in FIG. 4. A transmission hole 11 having the 
-Y direction as its gradually increasing direction may be arranged on the 
-Y direction side of a prohibited block 4i. Similarly, a transmission hole 
11 having the +X direction as its gradually increasing direction may be 
arranged on the +X direction side of a prohibited block 4i, and a 
transmission hole 11 having the -X direction as its gradually increasing 
direction may be arranged on the -X direction side of a prohibited block 
4i. 
In order to obtain the shaped beam B2, the rectangular beam B1 is 
irradiated over a part of the transmission hole 11 and a part of the 
prohibited block 4i which is adjacent to the block 4b in which this 
transmission hole 11 is provided. In this case, the transmission hole 11 
has a right-angled triangular shape and the shaped beam B2 thus has a 
right-angled triangular cross section. Accordingly, it is sufficient to 
provide one prohibited block 4i with respect to one transmission hole 11. 
Furthermore, the shape of the transmission hole 11 is of course not 
limited to the right-angled triangular shape and the transmission hole 11 
may have other shapes. 
The charged particle beam exposure method according to the present 
invention may be realized by the charged particle beam exposure apparatus 
shown in FIG. 1 by using the transmission mask according to the present 
invention having the above defined transmission hole and prohibited block. 
Next, a description will be given of a first embodiment of a charged 
particle beam exposure method according to the present invention which 
uses a first embodiment of a transmission mask according to the present 
invention, by referring to FIGS. 5A through 5C. In FIGS. 5A through 5C, 
those parts which are the same as those corresponding parts in FIG. 4 are 
designated by the same reference numerals, and a description thereof will 
be omitted. 
In FIGS. 5A through 5C, the right-angled triangular shape of the 
transmission hole 11 in the block 4b is identical to that of the 
transmission hole shown in FIG. 4. 
In FIG. 5A, a transmission hole 11 having the -X direction as its gradually 
increasing direction is arranged on the -X direction side of a prohibited 
block 4i. A transmission hole 11 having the -Y direction as its gradually 
increasing direction may be arranged on the -Y direction side of a 
prohibited block 4i as shown in FIG. 5B. A transmission hole 11 having the 
+X direction as its gradually increasing direction is arranged on the +X 
direction side of a prohibited block 4i as shown in FIG. 5C. 
In order to obtain the shaped beam B2 in FIG. 1, the rectangular beam B1 is 
irradiated over a part of the transmission hole 11 and a part of the 
prohibited block 4i which is adjacent to the block 4b in which this 
transmission hole 11 is provided. In this case, the transmission hole 11 
has a right-angled triangular shape and the shaped beam B2 thus has a 
right-angled triangular cross section. Accordingly, it is sufficient to 
provide one prohibited block 4i with respect to one transmission hole 11, 
and there is no need to provide a plurality of prohibited blocks with 
respect to one transmission hole. 
Next, a description will be given of a second embodiment of the charged 
particle beam exposure method according to the present invention which 
uses a second embodiment of the transmission mask according to the present 
invention, by referring to FIG. 6. In FIG. 6, those parts which are the 
same as those corresponding parts in FIG. 4 are designated by the same 
reference numerals, and a description thereof will be omitted. 
In FIG. 6, four transmission holes 11a through 11d respectively are 
provided within blocks 4b1 through 4b4 which surround the prohibited block 
4i. These transmission holes 11a through 11d have mutually different 
shapes. That is, the transmission hole 11a has a triangular shape, the 
transmission hole 11b has a trapezoidal shape, the transmission hole 11c 
has a parallelogrammic shape, and the transmission hole 11d has a 
right-angled triangular shape. 
The transmission hole 11a having the +Y direction as its gradually 
increasing direction is arranged on the +Y direction side of the 
prohibited block 4i, and the transmission hole 11b having the -Y direction 
as its gradually increasing direction is arranged on the -Y direction side 
of the prohibited block 4i. Similarly, the transmission hole 11c having 
the +X direction as its gradually increasing direction is arranged on the 
+X direction side of the prohibited block 4i, and the transmission hole 
11d having the -X direction as its gradually increasing direction is 
arranged on the -X direction side of the prohibited block 4i. 
In order to obtain the shaped beam B2 in FIG. 1, the rectangular beam B1 is 
irradiated over a part of a selected one of the transmission holes 11a 
through 11d and a part of the prohibited block 4i which is adjacent to the 
block 4b in which the selected transmission hole is provided. Accordingly, 
it is sufficient to provide one prohibited block 4i with respect to the 
four transmission holes 11a through 11d. In other words, one prohibited 
block 4i is shared by the four transmission holes 11a through 11d, so as 
to minimize the area in which no transmission hole may be provided. In 
addition, it is possible to increase the number of kinds of patterns to be 
formed by the transmission mask in this embodiment. 
Next, a description will be given of a third embodiment of the charged 
particle beam exposure method according to the present invention which 
uses a third embodiment of the transmission mask according to the present 
invention, by referring to FIGS. 7A and 7B. In FIGS. 7A and 7B, those 
parts which are the same as those corresponding parts in FIG. 6 are 
designated by the same reference numerals, and a description thereof will 
be omitted. 
In FIGS. 7A and 7B, four transmission holes 11a through 11d respectively 
are provided within blocks 4b1 through 4b4 which surround the prohibited 
block 4i. These transmission holes 11a through 11d have the same 
right-angled triangular shape but the arrangement of each right-angled 
triangular shape is rotated 90.degree. relative to the adjacent 
transmission hole. Further, only the arrangement of the right-angled 
triangular shape is different between FIGS. 7A and 7B, and a description 
will thus only be given with respect to FIG. 7A for the sake of 
convenience. 
In FIG. 7A, the transmission hole 11a having the +Y direction as its 
gradually increasing direction is arranged on the +Y direction side of the 
prohibited block 4i, and the transmission hole 11b having the -Y direction 
as its gradually increasing direction is arranged on the -Y direction side 
of the prohibited block 4i. Similarly, the transmission hole 11c having 
the +X direction as its gradually increasing direction is arranged on the 
+X direction side of the prohibited block 4i, and the transmission hole 
11d having the -X direction as its gradually increasing direction is 
arranged on the -X direction side of the prohibited block 4i. 
The shape of the transmission hole 11a is identical to that of the 
transmission hole 11d rotated 90.degree. clockwise. The shape of the 
transmission hole 11b is identical to that of the transmission hole 11d 
rotated 180.degree. clockwise. The shape of the transmission hole 11c is 
identical to that of the transmission hole 11d rotated 270.degree. 
clockwise. 
In order to obtain the shaped beam B2 in FIG. 1, the rectangular beam B1 is 
irradiated over a part of a selected one of the transmission holes 11a 
through 11d and a part of the prohibited block 4i which is adjacent to the 
block in which the selected transmission hole is provided. In this case, 
the transmission holes 11a through 11d have a right-angled triangular 
shape and the shaped beam B2 thus has a right-angled triangular cross 
section. Accordingly, it is sufficient to provide one prohibited block 4i 
with respect to the four transmission holes 11a through 11d. In other 
words, one prohibited block 4i is shared by the four transmission holes 
11a through 11d, so as to minimize the area in which no transmission hole 
may be provided. In addition, this embodiment is suited when exposing 
basic patterns which are rotated because the IC often includes a 
repetition of basic patterns and rotated patterns thereof. 
Next, a description will be given of a fourth embodiment of the charged 
particle beam exposure method according to the present invention which 
uses a fourth embodiment of the transmission mask according to the present 
invention, by referring to FIG. 8. In FIG. 8, those parts which are the 
same as those corresponding parts in FIG. 6 are designated by the same 
reference numerals, and a description thereof will be omitted. 
In FIG. 8, four transmission holes 11a through 11d respectively are 
provided within blocks 4b1 through 4b4 which surround the prohibited block 
4i. These transmission holes 11a through 11d have the same 
parallelogrammic shape but the arrangement of each parallelogrammic shape 
is such that the shapes of two mutually confronting transmission holes are 
symmetrical about the prohibited block 4i. 
In FIG. 8, the transmission hole 11a having the +Y direction as its 
gradually increasing direction is arranged on the +Y direction side of the 
prohibited block 4i, and the transmission hole 11b having the -Y direction 
as its gradually increasing direction is arranged on the -Y direction side 
of the prohibited block 4i. Similarly, the transmission hole 11c having 
the +X direction as its gradually increasing direction is arranged on the 
+X direction side of the prohibited block 4i, and the transmission hole 
11d having the -X direction as its gradually increasing direction is 
arranged on the -X direction side of the prohibited block 4i. 
The shape of the transmission hole 11c is identical to that of the 
transmission hole 11a rotated 90.degree. clockwise. The shape of the 
transmission hole 11d is identical to that of the transmission hole 11b 
rotated 90.degree. clockwise. The shape of the transmission hole 11b is 
obtained by inverting the shape of the transmission hole 11a about an 
imaginary center line Cx of the prohibited block 4i. In addition, the 
shape of the transmission hole 11d is obtained by inverting the shape of 
the transmission hole 11c about an imaginary center line Cy of the 
prohibited block 4i. 
In order to obtain the shaped beam B2 in FIG. 1, the rectangular beam B1 is 
irradiated over a part of a selected one of the transmission holes 
11athrough 11d and a part of the prohibited block 4i which is adjacent to 
the block in which the selected transmission hole is provided. 
Accordingly, it is sufficient to provide one prohibited block 4i with 
respect to the four transmission holes 11a through 11d. In other words, 
one prohibited block 4i is shared by the four transmission holes 11a 
through 11d, so as to minimize the area in which no transmission hole may 
be provided. In addition, this embodiment is suited when exposing basic 
patterns which are rotated and inverted because the IC often includes a 
repetition of basic patterns and rotated and/or inverted patterns thereof. 
Next, a description will be given of a fifth embodiment of the transmission 
mask according to the present invention, by referring to FIG. 9. In FIG. 
9, those parts which are the same as those corresponding parts in FIGS. 4 
through 8 are designated by the same reference numerals, and a description 
thereof will be omitted. 
In this embodiment, the transmission holes 11a through 11d are respectively 
provided within the blocks 4b1 through 4b4. The transmission holes 11a 
through 11d have the same triangular shapes, and the triangular shapes are 
arranged in the same manner as that shown in FIG. 7A. The prohibited block 
4i is surrounded by the four blocks 4b1 through 4b4 in which the 
transmission holes 11a through 11d are provided. In blocks 4b other than 
the blocks 4b1 through 4b4, transmission holes 11e are provided. Each 
transmission hole 11e is of the type which is irradiated by the 
rectangular beam B1 in its entirety, that is, the rectangular beam B1 
always passes through the entire transmission hole 11e and the size of the 
shaped beam B2 is not varied. 
Next, a description will be given of a sixth embodiment of the transmission 
mask according to the present invention, by referring to FIG. 10. In FIG. 
10, those parts which are the same as those corresponding parts in FIGS. 4 
through 9 are designated by the same reference numerals, and a description 
thereof will be omitted. 
In this embodiment, four transmission holes 11a through 11d are provided in 
the respective blocks 4b, and four alignment marks 11f are provided in the 
respective blocks 4b, in addition to the transmission holes 11e in the 
respective blocks 4b. Three sides of each block 4b in which the alignment 
mark 11f is provided is surrounded by the prohibited blocks 4i. One of the 
three prohibited blocks 4i surrounding the block 4b of the alignment mark 
11f is used in common as the prohibited block 4i provided with respect to 
one of the transmission holes 11a through 11d. In addition, each alignment 
mark 11f can be used similarly as the transmission holes 11a through 11d 
by irradiating the square beam B1 over only a part of the alignment mark 
11f. 
For example, assuming that the square beam B1 irradiates the prohibited 
block 4i which is immediately adjacent to both the alignment mark 11f and 
the transmission hole 11a, the cross sectional area of the shaped beam B2 
increases as the irradiating position of the square beam B1 is moved in 
the +Y direction. On the other hand, the cross sectional area of the 
shaped beam B2 increases as the irradiating position of the sequare beam 
B1 is moved in the +X direction. Hence, according to this embodiment, it 
is unnecessary to provide a prohibited block exclusively for each of the 
transmission holes 11a through 11d by effectively utilizing the prohibited 
blocks 4i which are already provided with respect to the alignment mark 
11f. 
In each of the embodiments, the cross sectional area of the square beam B1 
is approximately equal to the area of one block 4b. The cross sectional 
area of the square beam B1 may be slightly smaller than that of the block 
4b if the transmission hole 11 within each block 4b can be irradiated in 
its entirety by the square beam B1. On the other hand, the cross sectional 
area of the square beam B1 may be slightly greater than that of the block 
4b if the transmission hole 11 within the adjacent block block 4b will not 
be irradiated by the square beam B1. 
Further, the present invention is not limited to these embodiments, but 
various variations and modifications may be made without departing from 
the scope of the present invention.