Clearance measuring device and method for exposure

Optics: measuring and testing – By alignment in lateral direction – With registration indicia

Reexamination Certificate

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Details

C356S505000, C355S053000

Reexamination Certificate

active

06320659

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to clearance measuring devices and methods and, more specifically to a clearance measuring device and method used for adjusting a clearance between a photomask and a plate in an exposure apparatus.
2. Description of the Background Art
Recently, a method of transferring a pattern on a photomask onto a plate by exposure while ensuring a small clearance between the photomask and the plate has been widely used. Such an exposure method is called an off contact exposure method or proximity exposure method.
In the off contact exposure method and proximity exposure method, a clearance between a photomask and a plate must be measured and adjusted by a highly reliable method. For example, the clearance between the photomask and the plate is generally adjusted to be from 0.05 mm to 0.5 mm.
Now, a conventional method of measuring a clearance between a photomask and a plate will be described with reference to FIG.
12
. Shown in
FIG. 12
are a clearance measuring device
300
for measuring the clearance between the photomask and the plate, and plate
101
and photomask
102
spaced apart by a clearance G
5
.
Clearance measuring device
300
includes in a box
301
: a laser light source
302
for diagonally and downwardly directing light
302
a
to plate
101
and photomask
102
; and a light sensor
303
sensing the light reflected by plate
101
and photomask
102
.
Light
302
a
is divided into light
302
b
reflected by a surface
102
a
of photomask
102
which is opposite to plate
101
, and light
302
c
reflected by a surface
101
a
of plate
101
which is opposite to photomask
102
. Light
3
O
2
b
and
302
c
are sensed by light sensor
303
, and a distance S
5
between light
302
b
and
302
c
is calculated by a processor (not shown).
Here, as distance S
5
is proportional to clearance G
5
, clearance G
5
can be preliminary adjusted to provide a given distance S
5
.
However, conventional clearance measuring device
300
is expensive. If a plurality of clearance measuring devices
300
must be provided to measure the clearance between plate
101
and photomask
102
at a plurality of locations, the problem associated with a cost arises.
Further, conventional clearance measuring device
300
requires a processor in addition to the device used for aligning photomask
102
and plate
101
. As a result, the problem associated with the cost arises and the structure of the clearance measuring device becomes complicated.
Moreover, conventional clearance measuring device
300
requires laser light source
302
and light sensor
303
in addition to these at used for aligning photomask
102
and plate
101
. Thus, the structure of the clearance measuring device becomes complicated.
When the pattern on photomask
102
is transferred onto plate
101
by exposure, a mechanism for moving clearance measuring device
300
outside photomask
101
must be provided. Thus, the structure of the clearance measuring device becomes complicated.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a clearance measuring device and method capable of accurately and inexpensively measuring a clearance between a plate and a photomask.
Another object of the present invention is to provide a clearance measuring device and method capable of easily and inexpensively measuring a clearance between a plate and a photomask when the clearance is to be measured at a plurality of locations.
According to the present invention, a clearance measuring device is provided which measures a clearance between a photomask and a plate for adjusting it to a prescribed value based on the measurement data in an exposure apparatus transferring a pattern on the photomask onto the plate by exposing the plate to light through the photomask. The photomask has a mark used for measuring a clearance (hereinafter referred to as a clearance measuring mark) in a prescribed position on a surface opposite to the plate. The clearance measuring device includes: at least one light sensor sensing an image of the clearance measuring mark on the plate or a shadow of the clearance measuring mark projected on the plate when light is directed to the clearance measuring mark and a region including the clearance measuring mark; a processor calculating the clearance between the photomask and the plate based on a relative positional relationship between the image or shadow of the clearance measuring mark on the plate and the clearance measuring mark; and a clearance adjusting device adjusting the clearance between the photomask and the plate to a prescribed value by relatively moving the photomask and the plate based on the calculation result obtained by the processor.
According to the present invention, a clearance measuring method of an exposure apparatus transferring a pattern on a photomask having a clearance measuring mark onto a plate by exposing the plate to light through the photomask is provided in which the clearance between the photomask and the plate is measured and adjusted to a prescribed value based on a measurement data. In the clearance measuring method, the clearance between the photomask and the plate is calculated based on a relative positional relationship between an image or shadow of the clearance measuring mark on the plate and the clearance measuring mark when the light is directed to a region including the clearance measuring mark, and the clearance between the photomask and the plate is adjusted to a prescribed value by relatively moving the photomask and the plate based on the calculation result.
According to the clearance measuring device and method, when light is directed to the region including the clearance measuring mark on the photomask, a prescribed clearance between the photomask and the plate ensures the image or shadow of the clearance measuring mark on the plate.
The relative positional relationship between the clearance measuring mark of the photomask and the image or shadow of the clearance measuring mark, for example, an amount of displacement thereof, changes in accordance with the clearance between the photomask and the plate. In other words, the displacement between the clearance measuring mark of the photomask and the image or shadow of the clearance measuring mark is proportional to the clearance between the photomask and the plate.
Thus, the clearance measuring mark on the photomask and the image or shadow of the clearance measuring mark are sensed by the light sensor, and an amount of displacement of the clearance measuring mark on the photomask and the image or the shadow of the clearance measuring mark or the like can be calculated by the processor performing for example an image process.
As a result, the clearance between the photomask and the plate can accurately be adjusted to a prescribed value by the clearance adjusting device based on the calculation result.
Further, to implement the clearance measuring device and method in a more preferred manner, the clearance between the photomask and the plate may accurately be adjusted to a prescribed value by the clearance adjusting device based on an amount of difference in shape between the clearance measuring mark and the image or shadow of the clearance measuring mark or the like.
Preferably, an alignment mark for aligning the photomask and the plate or a portion of the pattern on the photomask to be transferred onto the plate may be used as the clearance measuring mark. Thus, the clearance measuring device and method of the present invention are achieved without increasing the number of patterns to be formed on the photomask.
Preferably, the light sensor is used which is provided with a mechanism movable in X and Y directions of the photomask. Thus, the light sensor can move in X and Y directions of the photomask, so that the clearance between the plate and the photomask can readily be measured at a plurality of locations.
To implement the clearance measuring device and method in a more preferred manner, the light sensor may be provided with a mechani

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