Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
1999-10-21
2003-06-03
Lee, John R. (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S492220, C250S491100, C250S492240
Reexamination Certificate
active
06573516
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electron-beam lithography system, or more particularly, to an electron-beam lithography system for drawing patterns using an electron beam by continuously moving a stage.
2. Description of the Related Art
With advancement in a microprocessing technology, the trend of semiconductor integrated circuits is toward very dense integrated circuits. The performance which the microprocessing technology is required to offer must be severely evaluated. Among lithography technologies, the photolithography technology implemented in a step-and-repeat photolithography system with demagnification or the like in the past is expected to reach its limits in the near future. An electron-beam lithography technology is expected to take over from photolithography technology and be used for a new generation of microprocessing.
The drawbacks of the electron-beam lithography technology, been pointed out in the past, are low processing speed and poor manufacturing efficiency. For conventional electron-beam lithography systems, similarly to the step-and-repeat photolithography system with demagnification, a step-and-repeat photolithography method with demagnification has been adopted. According to this method, a sample (wafer) is placed on a stage. After a predetermined area is exposed and thus patterned, the stage is moved in order to expose a subsequent area for patterning. This procedure is repeated, whereby the whole sample is exposed and thus patterned. For example, one wafer is exposed to produce 60 chips each having a width of 15 mm. In this case, since an area in which an electron beam can be deflected is approximately 1.5 mm in width, the stage must be moved 100 times in order to produce each chip. For a whole wafer, the stage must be moved 6000 times. Exposure cannot be carried out while the stage is moved or until an irradiated position to which an electron beam is irradiated and which is changed with movement of the stage is determined accurately. This time interval shall be referred to as a stage settlement wait time herein. Movements of the stage are mechanical. For precise movement, therefore, it takes some time. The stage settlement time is therefore considerably long, or at present, about 0.5 sec. The time required for moving the stage 6000 times is as much as 50 min. There is therefore a difficulty in improving the processing speed.
Development of various technologies is under way in efforts to improve a throughput. A continuous movement lithography (stage scan) method is one example of these technologies. According to this method, the stage is moved continuously for exposure. FIG.
1
A and
FIG. 1B
are explanatory diagrams concerning the continuous movement lithography method.
FIG. 1A
is concerned with a method of exposing a wafer with the stage being moved in one direction, while
FIG. 1B
is concerned with a method of exposing the wafer with the stage being advanced and returned in opposite directions.
As illustrated, a plurality of chips
90
is produced from a sample (wafer)
18
. Only four chips are shown in the drawings. Normally, several tens to several hundreds of chips are produced. As mentioned above, an area in which an electron beam can be deflected is smaller than each chip
90
. Each chip
90
is therefore segmented into a plurality of areas
91
and then exposed. According to the step-and-repeat photolithography method with demagnification, when the stage is moved to the center of each area, the area is exposed. In contrast, according to the continuous movement lithography method, as illustrated, the areas
91
that are aligned on the same column in the same column of chips
90
are exposed by moving the stage. In other words, an exposed area is segmented into a plurality of rectangular areas extending over the borders among chips. The stage is moved continuously over the rectangular areas. According to this method, the stage settlement wait time can be nullified and the processing speed can be improved. For example, assuming that the area in which an electron beam can be deflected is approximately 1.5 mm wide, an area having dimensions of 1.5 mm×ten several centimeters can be patterned during a single scan without the necessity of taking a stage settlement wait time. The total stage settlement wait time is therefore decreased to about {fraction (1/100)}. The processing speed therefore improves greatly. For methods of scanning a wafer with an electron beam to pattern it, the continuous movement lithography method can be said to be an essential technology. According to the continuous movement lithography method, a sample moves during patterning. The position of an electron beam must therefore be corrected accordingly. Controlling the position of an electron beam is therefore more complex than that according to the step-and-repeat photolithography method with demagnification. The continuous movement lithography method falls into the method of exposing a wafer with a stage being moved in one direction as shown in
FIG. 1A
, and the method of exposing a wafer with the stage being advanced and returned in opposite directions as shown in FIG.
1
B. The method shown in
FIG. 1B
offers a higher processing speed because it is unnecessary to return to one extreme end. However, since backlash and the like pose a problem, a high-precision moving mechanism is needed.
FIG. 2
shows the configuration of an electron-beam lithography system for performing lithography according to the continuous movement lithography method. In
FIG. 2
, there are shown a processor
1
, a magnetic disk
2
, and a magnetic tape drive
3
. These units are interconnected over a bus
4
, and connected to a data memory
6
and stage control circuit
7
via an interface circuit
5
over the bus
4
.
A housing (column)
8
accommodates an electron gun
9
, a lens
10
, a blanking electrode
11
, a lens
12
, a feedback coil
13
, a sub-deflector coil
14
, a lens
15
, a main deflector coil
16
, a stage
17
, and a sample
18
. The sample (wafer)
18
is placed on the stage
17
. The stage
17
is moved in the X and Y directions according to an output signal of the stage control circuit
7
.
Moreover, data read from the data memory
6
is supplied to a pattern correction circuit
20
via a pattern generation circuit
19
. The pattern correction circuit
20
applies a blanking signal to the blanking electrode
11
via an amplifier
21
. Moreover, the pattern correction circuit
20
applies a signal to the coils
13
,
14
, and
16
via D/A converters (DAC)
22
,
24
, and
26
and amplifiers
23
,
25
, and
27
.
An electron beam radiated from the electron gun
9
passes through the lens
10
. The electron beam is then transmitted or intercepted by the blanking electrode
11
, and reshaped into a rectangular beam of parallel rays having any spot size of, for example, 3 &mgr;m or less. Thereafter, the feedback coil
13
, sub-deflector coil
14
, and main deflector coil
16
deflect the electron beam. The electron beam is then converged on the surface of the sample through the projection lens
15
. Areas where the feedback coil
13
, sub-deflector coil
14
, and main deflector coil
16
can deflect the beam get larger in that order. Specifically, the area where the feedback coil
13
can deflect the beam is smaller than that where the sub-deflector coil
14
can. The area where the sub-deflector coil
14
can deflect the beam is smaller than that where the main deflector coil
16
can. For ensuring a large area where the beam can be deflected, the number of windings of a coil must be increased accordingly. The response speeds of the coils get lower in reverse order. In other words, a settlement wait time required by the feedback coil
13
is the shortest. Settlement wait times required by the sub-deflector coil
14
and main deflector coil
16
get longer in that order. In the foregoing configuration, the exposed areas
91
shown in FIG.
1
A and
FIG. 1B
correspond to the area where the main deflector coil
16
ca
Advantest Corporation
Christie Parker & Hale LLP
Fernandez Kalimah
Lee John R.
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