Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
2003-03-18
2004-05-25
Mathews, Alan (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C356S400000, C356S401000
Reexamination Certificate
active
06741330
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an exposure device which has a microscope for determining mask alignment marks and a microscope for determining workpiece alignment marks and in which, using the two microscopes, positioning of the mask alignment marks and the workpiece alignment marks relative to one another is carried out. The invention relates especially to an exposure device in which the workpiece is divided into several exposure zones and which is used as an exposure device for incremental exposure of each exposure zone in a suitable manner.
2. Description of the Prior Art
In the production of a device for producing a semiconductor, a process is carried out in which a mask pattern which has been formed on a mask is exposed onto a wafer (hereinafter called a “workpiece”) as the substrate which is to be treated. In this process, the following is steps are performed:
the area to be exposed on the wafer is divided into several areas;
the mask pattern is projected onto the above described areas which have been produced by division;
a workpiece carrier on which the wafer has been seated is moved by a given amount; and
the above described exposure areas which have been formed by division are moved in rows to the exposure position and incrementally exposed.
This process is generally called incremental exposure or “step and repeat” exposure. An exposure device which carries out this exposure is called an “incremental exposure device” or “stepper” (hereinafter called an “incremental exposure device”).
The arrangement and operation of the above described incremental exposure device is described below using FIG.
6
. In this figure, the frame and the like which support the respective material components are not shown. In the figure, a light irradiation part
10
, from which exposure light emerges, has an optical system, such as a lamp
10
a
, a focusing mirror
10
b
and the like.
The exposure light emerging from the light irradiation part
10
is emitted onto a mask M on a mask carrier
11
. The mask pattern which has been formed on the mask M is imaged via a projection lens
12
onto a workpiece W on a workpiece carrier
13
and exposed. On the workpiece carrier
13
, there is a device
13
a
for movement in the X-Y directions (XY are two orthogonally intersecting axes on a plane which is perpendicular to the page of the drawing). By incrementally moving the workpiece carrier
13
, the workpiece W is moved from one area to the other area, which areas are formed by division, and thus, the workpiece W is exposed. If necessary, there can be a device for moving the workpiece carrier
13
in the &thgr;-Z direction (&thgr;: rotation around an axis perpendicular to the X-Y plane, Z: direction of the optical axis of the exposure light). Regulation of the imaging position of the mask pattern is carried out by movement either of the mask M, the projection lens
12
or the workpiece carrier
13
in the direction of the optical axis (Z-direction).
Before exposure of the workpiece W, positioning of the mask M relative to the workpiece W is carried out in order to expose the mask pattern at a given position of the workpiece W. This positioning is carried out by determining the positions of mask alignment marks MAM formed in the mask (hereinafter called mask marks) and the workpiece alignment marks WAM formed in the workpiece W (hereinafter called workpiece marks) and by moving the mask M and/or the workpiece W such that the two marks attain a given positional relationship (for example, are aligned with one another).
Therefore, there are two microscopes
14
for determining the mask marks (hereinafter called “microscopes for mask marks”) which determine the mask marks MAM, and one microscope
15
for determining the workpiece marks (hereinafter called the “microscope for workpiece marks”) which determines the workpiece marks WAM.
The microscopes for mask marks
14
are positioned to be removable or insertable between the light irradiation part
10
and the mask M. The position relationship of the two microscopes for mask marks
14
is set beforehand and the coordinate systems of the two microscopes agree with one another. Normally, there are two microscopes for mask marks
14
. The reason for this is to determine two mask marks MAM at the same time, to measure the deviation of the mask M in the &thgr; direction and to correct the amount of deviation. If there is a device for extensive movement of the microscope for mask marks
14
in the X-Y directions, only one microscope for mask marks
14
is sufficient. However, the mask carrier
11
is normally not made such that it can move to a large extent. If it is made such that it can move to a large extent, the precision of the movement is problematical and the arrangement of the devices complicated. Therefore, normally two microscopes for mask marks
14
are used.
In the microscope for mask marks
14
, there is an alignment light source
14
a
which emits alignment light. The alignment light is reflected via the mask M and the projection lens
12
by workpiece W or by the workpiece carrier
13
when the mask M is present, and via the mask M if again the mask M and projection lens
12
are present, enters the CCD camera
14
b
of the microscope for mask marks
14
.
The microscope for workpiece marks
15
is located integrally with a projection lens
12
. In the microscope for workpiece marks
15
, there is also an alignment light source
15
a
which emits alignment light. The alignment light is reflected by the workpiece W or the workpiece carrier
13
and enters the CCD camera
15
b
of the microscope for workpiece marks
15
. Here, it is assumed that, with respect to the X-Y directions of motion of the workpiece carrier
13
, there is square parallelism of the X-Y coordinates of the two microscopes
14
for the mask marks and of the microscope
14
for the workpiece marks
15
. The pictures which have been received by the CCD cameras
14
b
,
15
b
, which are located in the microscopes
14
,
15
, are sent to a controller
16
. The controller
16
acquires the position information of the respective mark by image processing of the determined mask marks MAM or the workpiece marks WAM.
The sequence of positioning of the mask relative to the workpiece in the above described exposure device is described below.
(1) Base Line Correction
In the exposure device shown in
FIG. 6
, the microscope for determining the mask marks and the microscope for determining the workpiece marks differ from one another. Therefore, the mask and the workpiece cannot be positioned relative to one another if the position relationship of the two with respect to each other is not known exactly.
Furthermore, since the positional relationship of the two with respect to one another is changed by thermal expansion which is caused by the ambient conditions and the like of the device, generally confirmation and correction must be carried out. This activity of correction of the relative positions of the microscope for mask marks
14
and of the microscope for the workpiece marks
15
relative to one another is called “baseline correction” here.
(i) As shown in FIG.
7
(
a
), in the workpiece carrier
13
a reference mark BM (only one mark is sufficient) is formed.
(ii) The workpiece carrier
13
is moved to a preset position such that the above described reference mark BM extends into the field of vision of one of the microscopes
14
for the mask marks. The microscope for mask marks
14
emits alignment light. The reference mark BM is illuminated via the projection lens
12
. The light reflected by the reference mark BM is received via the projection lens
12
by the CCD camera
14
b
of the microscope
14
for mask marks. FIG.
7
(
a
) shows the reference marks BM received by the CCD camera
14
b.
(iii) The reference mark image received by the CCD camera
14
b
is sent to the controller
16
and is subjected to image processing. Thus, the position of the microscope
14
for the mask marks is computed at the coordinates and stored in the co
Mathews Alan
Nixon & Peabody LLP
Safran David S.
Ushiodenki Kabushiki Kaisha
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