Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
1999-10-27
2001-07-03
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C318S135000
Reexamination Certificate
active
06256085
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an exposure apparatus for manufacturing devices such as semiconductor elements and liquid crystal elements.
FIG. 2
shows the schematic arrangement of a conventional semiconductor exposure apparatus. Referring to
FIG. 2
, reference numeral
10
denotes an illumination optical unit;
11
, a reticle (original plate);
12
, a reticle stage;
13
, a projection optical unit;
14
, a wafer (exposure target); and
15
, a wafer stage. The illumination optical unit
10
includes an exposure light source. As the light source, a mercury lamp, a KrF excimer laser, or the like is used. A circuit pattern to be exposed is drawn on the glass surface of the reticle
11
. The reticle
11
is mounted on the reticle stage
12
. The pattern of the reticle
11
is to be transferred to the wafer
14
. The wafer stage
15
can move with the wafer
14
being mounted on it.
The operation of the exposure apparatus will be described. Light from the illumination optical unit
10
is guided to the reticle
11
positioned by the reticle stage
12
, is transmitted through the projection optical unit
13
, and is transferred (exposed) onto the wafer
14
. In the exposure apparatus, the wafer stage
15
performs positioning at a desired position within a plane. When the above exposure is repeated, the pattern of the reticle
11
is exposed onto the wafer
14
a plurality of times.
Usually, a semiconductor element is fabricated not by only exposure using one reticle
11
, but by performing exposure a plurality of times in an overlapping manner on the same wafer while exchanging the reticle
11
. For this purpose, the wafer once exposed must be mounted on the wafer stage
15
again and be precisely aligned with the reticle
11
. The semiconductor exposure apparatus has an aligning function for this. According to a typical method, an alignment mark used for alignment is exposed in advance, and this alignment mark is observed with a microscope
16
, thereby performing alignment.
In both exposure and alignment described above, the positions of the reticle stage
12
and wafer stage
15
must be held precisely. If a positioning error is large, the circuit pattern is transferred to be displaced from the pattern on the reticle, so desired circuit characteristics cannot be obtained. The same inconvenience also occurs when a positioning error occurs during alignment. Therefore, the positioning performance of the two stages is a significant performance index directly associated with the performance of the exposure apparatus.
Each stage is positioned within the plane by positioning control performed by a position measurement unit
17
using a laser interferometer or the like.
FIG. 3
is an illustration of a positioning control unit. The positioning control unit is constituted by a feedback loop. In the feedback loop, a difference between position information x obtained by the position measurement unit
17
and a target position r is calculated. The calculated difference is subjected to an appropriate compensating calculation by a compensator
18
to form a drive instruction value for the wafer stage
15
. Along with the recent development of microprocessors, this feedback loop is often constituted by a software servo mainly including a digital filter.
Generally, the measurement axis of the position measurement unit
17
is arranged to coincide with the optical central position constituted by the projection optical unit
13
, i.e., the exposure center. This is because the exposed position must be held precisely. In other words, for example, the wafer stage
15
is controlled on a coordinate system having an exposure central position as the reference.
A case wherein a disturbance is applied to the wafer stage
15
will be considered. For example, the vibration of the building where the exposure apparatus is installed, or a reaction produced when the wafer stage
15
itself moves, may excite the main body structure on which the wafer stage is mounted (i.e., the position measurement unit
17
). Such a disturbance includes not only a component of one direction but also a translational component and a rotational component. Even if only a translational component is applied as the disturbance, a disturbance in a rotational direction is sometimes excited as another component. Inversely, even if only a rotational component is applied as the disturbance, a disturbance in a translational direction is sometimes excited as another component.
When these disturbance components are generated, the wafer stage
15
operates to suppress them with the feedback loop. According to the basic performance of the exposure apparatus, a sufficiently high positioning performance must be guaranteed even when a disturbance of a certain degree is applied.
As described above, the disturbance is suppressed merely with reference to the exposure center. Accordingly, a sufficiently high positioning performance is guaranteed only from the viewpoint of the exposure central position.
Concerning alignment, it is often performed through observation of an alignment mark on an axis not coinciding with the exposure center, as described in the prior art. In this case, the alignment precision is regulated by the positioning performance with reference to the alignment mark observation position.
A case wherein a disturbance in a rotational direction is applied during alignment will be considered. Even if a sufficiently high positioning precision is obtained with reference to the exposure central position, it cannot be necessarily obtained at the mark observation position. This is because of the following reason. Assume that a positioning precision in a rotational direction at the exposure central position is guaranteed within a target value ±0.1 ppm. If the distance between the exposure central position and the mark observation position is 50 mm, since the rotational angle is small, an approximate calculation reveals that an alignment error or an error from an observation result of 50×0.1×10
−6
=5 nm occurs. In this manner, to guarantee a sufficiently high positioning precision on a coordinate system having the exposure center as the reference does not directly guarantee completely the same precision in alignment, leading to a problem.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the problems of the prior art described above, and has as its object to provide an exposure apparatus which can guarantee a uniform positioning precision regardless of the operating state of the apparatus. In order to achieve this object, the exposure apparatus according to the present invention has the following arrangement.
That is, there is provided an exposure apparatus for optically transferring a pattern drawn on an original plate onto an exposure target, comprising means for determining an operating state of the apparatus to determine a coordinate origin as a reference when positioning an exposure target stage which is movable with an exposure target being mounted thereon, means for switching the coordinate origin as the positioning reference, when necessary, that matches an operation of the apparatus on the basis of determination, and means for controlling positioning of the exposure target stage in accordance with coordinate information with reference to the switched coordinate origin.
There is also provided an exposure apparatus for optically transferring a pattern drawn on an original plate onto an exposure target, comprising means for determining an operating state of the apparatus to determine a coordinate origin as a reference when positioning an original plate stage which is movable with an original plate being mounted thereon, means for switching the coordinate origin as the positioning reference, when necessary, that matches an operation of the apparatus on the basis of determination, and means for controlling positioning of the original plate stage in accordance with coordinate information with reference to the switched coordinate origin.
There is
Adams Russell
Canon Kabushiki Kaishi
Fitzpatrick ,Cella, Harper & Scinto
Nguyen Hung Henry
LandOfFree
Exposure apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Exposure apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Exposure apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2487653