Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
2000-08-30
2003-06-03
Lee, John R. (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S492210
Reexamination Certificate
active
06573519
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an electron beam exposure apparatus of a block exposure type, an adjusting method, and a block mask for the adjustment or, in particular, to the adjustment of a mask deflector to select a pattern of the block mask.
There is a general trend that the density of semiconductor integrated circuits increases depending on advances in micro-machining technology, and the performance required for the micro-machining technology becomes more and more severe. Particularly, in exposure technology, the limit of the optical exposure technology used for devices such as a conventional stepper has been reached. The electron beam exposure technology may be used instead of the optical exposure technology for the advanced micro-machining technology.
There are several types of the electron beam exposure apparatuses such as the variable rectangle exposure type, the block exposure type, and the multibeam exposure type. The present invention relates to the block exposure type. In the block exposure type, a repetitive figure is exposed by integrating unit patterns generated at one time by an electron beam passing through a transmission mask having unit patterns of the repetitive figure.
FIG. 1
illustrates a configuration of a beam radiation system of the block exposure type electron beam exposure apparatus. In
FIG. 1
, reference number
11
refers to an electron gun that generates an electron beam,
12
to a first convergent lens that forms the electron beam from the electron gun
11
into a parallel beam,
13
to an aperture that shapes the parallel beam passing through into a specified shape,
14
to a second convergent lens that converges the formed beam,
15
to a deflector for shaping,
16
to a first mask deflector,
17
to a deflector that dynamically compensates for the astigmatism of a mask,
18
to a second mask deflector,
19
to a convergent coil for a mask,
20
to a first shaping lens,
21
to a block mask moved by a stage
21
A,
22
to a second shaping lens,
23
to a third mask deflector,
24
to a blanking deflector for on/off control of the beam,
25
to a fourth mask deflector,
26
to a third shaping lens,
27
to a circular aperture,
28
to a reducing lens,
29
to a focus coil,
30
to a projection lens,
31
to an electromagnetic main deflector,
32
to an electrostatic sub-deflector, and
33
to a reflected electron detector that detects an electron radiated onto a specimen and reflected thereby, and a unit that includes all the parts mentioned above is called an electronic optical lens barrel (column). The electron beam
10
from the column is radiated toward a specimen (wafer)
1
placed on the stage
2
. The stage moves the wafer
1
two-dimensionally in a plane perpendicular to the electron beam
10
. The electron beam exposure apparatus is further equipped with an exposure control portion that controls each portion of the column in order to expose a desired pattern.
FIG. 2
illustrates the block mask
21
mentioned above. The block mask
21
looks like a silicon substrate such as a wafer, and the block mask area where an actual aperture pattern is formed is machined by etching or the like so that the depth is about 20 &mgr;m. In the block mask area, plural aperture patterns
61
are arranged in a matrix form as shown in the figure. The range in which the electron beam is deflected by the mask deflector to select the aperture pattern
61
is limited, and the size of the block mask area is determined accordingly. Each aperture pattern
61
has apertures
62
corresponding to the unit pattern of a repetitive figure. Though each aperture pattern
61
has different aperture patterns generally, plural apertures of the same shape are provided when the aperture pattern is used frequently. When a pattern is comprised of a combination of unit patterns only, it can be drawn by selecting and exposing the aperture pattern
61
. Generally it is difficult, however, to form a pattern using only unit patterns, therefore, an aperture pattern
61
consisting of an entire aperture is provided so that any pattern can be drawn by shaping the electron beam that has passed using a variable rectangle method.
Moreover, plural block mask areas are provided on a block mask and the block mask area to be used can be changed by moving the block mask
21
by the stage
21
A. This is because the aperture pattern may be damaged due to radiation by an electron beam over time.
To select the aperture pattern
61
, the beam is deflected by the first mask deflector
16
according to the position of the aperture pattern
61
to be selected, then the beam is made parallel again with the optical axis by the second mask deflector
18
, and put into the selected aperture pattern
61
perpendicularly. The beam that has passed through the selected aperture pattern
61
is deflected by the third mask deflector
23
so as to return to the optical axis, and the beam returned to the optical axis is deflected by the fourth mask deflector
25
so as to be made parallel to the optical axis. That is, the second mask deflector
18
and the third mask deflector
23
deflect the beam by the same amount but in the opposite direction as that of the first mask deflector
16
, and the fourth mask deflector
25
deflects the beam by the same amount as that of the first mask deflector
16
.
FIGS. 3A through 3C
illustrate the size of the beam compared with the aperture pattern
61
and the influence of the deviation of the deflection position.
As shown in
FIG. 3A
, plural square aperture patterns
61
are arranged in a matrix form on the block mask
21
. In addition to squares, rectangles may be used. The deflected beam passes through one of the plural aperture patterns
61
, but a beam of large size may pass through an aperture of other proximate aperture patterns. Furthermore, an error of the deflection amount by the first mask deflector
16
may also cause the beam to pass through an aperture of other proximate aperture patterns similarly. To prevent this, the beam is made to be about the same size as the aperture pattern
61
, a maximum aperture area circumscribed by a broken line is provided to the aperture pattern
61
, and the aperture is formed within this maximum aperture area. This will prevent the beam from passing through an aperture of other proximate apertures as long as the deviation of the deflection position is small. For example, if the length of a side of the square aperture pattern
61
is P and that of a side of the maximum aperture area, which is arranged in the center of the aperture pattern
61
, is Q, then the distance R between the side of the aperture pattern
61
and that of the maximum aperture area is (P−Q)/2. As shown in
FIG. 3B
, the beam does not pass through an aperture of other proximate aperture patterns as long as the error of the beam position is within ±R.
Since there is actually an error of the beam size, and the intensity at the edges changes gradually, it is preferable to adjust the side of the beam so as to be smaller than that of the aperture pattern
61
.
As shown in
FIG. 3C
, however, the distribution of intensity is not uniform in the beam, and the intensity is the strongest in the center and it becomes weaker at the peripheral portion. Therefore, there exists the difference S in intensity even though the deflection position of the beam is correct and the center of the beam coincides with that of the aperture pattern
61
. This difference S in intensity causes the variations in amount of exposure. Therefore, a beam with small variation is generated, and the sizes of the beam and aperture pattern, and the maximum aperture area, are determined with the variation being taken into account.
As mentioned above, due to the variation in the beam intensity, a portion of the beam with rather weak intensity may pass through the maximum aperture area of the selected aperture pattern, and the variation of the beam becomes larger after it passes through the aperture, if the position of the beam is deviated. Therefore, it is
Advantest Corporation
Christie Parker & Hale LLP
Fernandez K
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