Optics: measuring and testing – By alignment in lateral direction – With registration indicia
Reexamination Certificate
1999-02-12
2002-03-19
Evans, F. L. (Department: 2877)
Optics: measuring and testing
By alignment in lateral direction
With registration indicia
C356S400000, C250S548000
Reexamination Certificate
active
06359688
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a projection exposure apparatus used when manufacturing a semiconductor chip, a liquid crystal panel, a CCD, a thin-film magnetic head or a micromachine, etc., by means of photolithography. More particularly, the invention relates to a projection exposure apparatus having means for adjusting deviation between the substrate surface of a mask or the substrate surface of a semiconductor wafer or the like, which is for manufacturing a device such as a semiconductor device or liquid crystal device, and the imaging plane of a projection optical system. The invention further relates to a method of manufacturing a device.
When a semiconductor device or liquid crystal device is manufactured by photolithography, use is made of a semiconductor exposure apparatus to transfer a pattern, which is drawn on a reticle serving as a original plate, onto a wafer coated with a photosensitive material.
A so-called step-and-repeat demagnifying-projection-type semiconductor exposure apparatus is employed at many production facilities as the semiconductor exposure apparatus according to the prior art. Such an apparatus moves each of a plurality of exposure areas (shot areas) of a wafer into the exposure field of the projection optics in successive fashion and exposes each of the shot areas to a reticle circuit pattern in one batch. However, enlarging the size of semiconductor chips has become the trend in recent years and, as a result, there is a growing demand for a larger exposure surface area in a semiconductor exposure apparatus in order that a pattern of a larger area on a reticle may be transferred to a wafer. At the same time, there is a need to improve the resolving power in order to deal with finer patters on semiconductor devices. A problem with the prior art, however, is that it is difficult technically to design and manufacture a demagnifying-projection-type semiconductor exposure apparatus that satisfies both the requirements of improved resolving power and larger exposure area.
In order to solve this problem, a scanning-type projection exposure apparatus has been developed. This apparatus successively exposes a wafer to a pattern image, which has been drawn on a reticle, by scanning the reticle with respect to a slit-shaped illumination area and scanning the wafer at the same time as the reticle with respect to an exposure area serving also as the illumination area. In the scanning-type projection exposure apparatus, a reticle stage holding the reticle and a wafer stage holding the wafer, which is a photosensitive substrate, are synchronously scanned relative to the projection optics in a mutually opposing direction and at a velocity ratio that conforms to the projection magnification, thereby exposing the wafer to light.
In order to improve the throughput in both types of semiconductor exposure apparatus, the reticle stage and wafer stage must be driven at a high acceleration and high speed. Accordingly, it has not been possible to avoid vibration of structural members including a lens barrel (referred to as the projection optical system or projection optics below), which accommodates a group of projection lenses. Unfortunately, such vibration lengthens the time needed for stabilization of positioning or scanning and degrades exposure performance.
First, it is noteworthy that vibration of structural members brought about by a driving reaction force disturbs positioning stabilization of the reticle or wafer. The reason for this is that a laser interferometer serving as position measurement means for measuring the position of the reticle or wafer stage is mounted on a structural member. More specifically, since the position measurement means vibrates owing to vibration of the structural member, each stage also vibrates, as a result of which it takes longer for positioning to stabilize. Accordingly, positioning stabilization is facilitated by feeding back, to the inputs of the respective stage drivers, outputs from acceleration sensors provided on structural members in close proximity to the stages. This technique is already known and is disclosed in detail in the specification of Japanese Patent Application Laid-Open (KOKAI) No. 10-12513 entitled “Scanning-type Projection Exposure Apparatus”. This control technique ascertains the vibration of a surface plate caused by stage vibration and moves the stage while following up this vibration, thereby eliminating positioning error.
Described next will be degradation of exposure performance caused by vibration due to the driving reaction force.
First, vibration due to the driving reaction force causes vibration not only of structural members such as the surface plate directly supporting the stage itself but also of the projection optical system, which is the heart of the projection apparatus. The mode of vibration of the projection optical system naturally is different from that of a structural member such as the surface plate directly supporting the stage. The projection optical system, which is a generally columnar structural member, usually is disposed in a vertical attitude and is mechanically connected to a structural member of the main body at a connecting portion referred to as a flange. Accordingly, a lower order mode of vibration that has a great effect upon exposure performance is one that would cause the columnar projection optical system to wobble. For example, in a case where a semiconductor exposure apparatus is of the scanning type, it is important that the wafer be exposed to a quiescent reticle circuit pattern by synchronously scanning the reticle and wafer at a predetermined velocity ratio. If the projection optical system is vibrating at this time, the circuit pattern also will vibrate on the wafer and, hence, projection precision will decline.
The effects of vibration of the projection optics, which is caused by stage vibration, on exposure precision will now be described with reference to the drawings.
FIG. 1
illustrates a scanning-type semiconductor projection apparatus, which is one embodiment of the present invention. As shown in
FIG. 1
, illuminating light IL emitted by a light source
1
is acted upon by a mirror
2
, a reticle blind
3
, a relay lens
4
, a mirror
5
and a condenser lens
3
and illuminates a reticle
7
with a uniform illuminance and over a slit-shaped illumination area decided by the reticle blind
3
. A reticle stage
8
is supported on a reticle stage surface plate
9
, and a reticle interferometer
11
is provided for sensing the position of the reticle stage
8
by projecting a laser beam LB onto a moving mirror
10
on the reticle stage
8
and then receiving the reflected light. The reticle stage
8
is staged to the left and right (along the direction of the y axis) in FIG.
1
.
A projection optical system PO is disposed below the reticle stage
8
and projects, in a reduced size, the circuit pattern of reticle
7
onto a wafer W, which is a photosensitive substrate, at a predetermined demagnification. The wafer W is held by a precision stage
12
a
on the top of a wafer stage
12
moved two-dimensionally in a horizontal plane. The position of the wafer stage
12
can be sensed by using a wafer laser interferometer
14
, which irradiates a moving mirror
13
with a laser beam LB and receives the reflected light. The wafer stage
12
is mounted on the wafer stage surface plate
15
.
During an exposure operation, the wafer stage
12
is scanned in sync with the reticle stage
8
in a direction opposite that of the reticle stage
8
along the y axis in FIG.
1
. Reaction forces produced by driving both stages cause vibration of the structural members of the main body, which include the reticle stage surface plate
9
and wafer stage surface plate
15
. This causes vibration also of the projection optical system PO, which is one of the structural members of the main body.
The influence of vibration-induced error that develops in the measurement signals from the reticle interferometer
11
and wafer laser interferometer
14
can be ascertain
Akimoto Satoshi
Uzawa Shigeyuki
Wakui Shinji
Evans F. L.
Smith Zandra V.
LandOfFree
Projection exposure apparatus and method of controlling same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Projection exposure apparatus and method of controlling same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Projection exposure apparatus and method of controlling same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2831751