Metal working – Method of mechanical manufacture – Work holding
Reexamination Certificate
2001-10-31
2003-09-09
Wilson, Lee D. (Department: 3723)
Metal working
Method of mechanical manufacture
Work holding
26, 26
Reexamination Certificate
active
06615477
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based on and claims priority on Japanese patent application 2001-167209, filed on Jun. 1, 2001, the whole contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
A) Field of the Invention
The present invention relates to a method and apparatus for processing a workpiece by using an X-Y stage, and more particularly to a method and apparatus for processing a workpiece capable of high position accuracy of a workpiece placed on and fixed to an X-Y stage.
B) Description of the Related Art
Fine patterns of reticles and masks used for photolithography processes of semiconductor integrated circuit devices are written by an electron beam, a laser beam or the like. A plurality of unit areas (fields) are defined on the plane of a substrate of a reticle or mask. For example, a desired pattern can be written in one unit area by scanning an electron beam. Desired patterns can be written in all unit areas by fixing a substrate to an X-Y stage and moving the substrate in an X-Y plane.
Generally, a plurality of unit areas are disposed in a matrix in the plane of a substrate on which desired patterns are written. A substrate is fixed to the X-Y stage so that the row and column directions along which unit areas are disposed are made in parallel to the X- and Y-axes of the X-Y stage. A plurality of columns disposed along the X-axis direction and a plurality of rows disposed along the Y-axis direction are respectively given sequential numbers starting from 1, and a unit area at the column number i and the row number j is represented by U (i, j).
A pattern is written first in the unit area U (1, 1), and then the X-Y stage is moved along the Y-axis direction to thereafter write a pattern in the unit area U (1, 2). This operation sequence is repeated to write patterns in all unit areas of the first column. After the patterns are written in all unit areas of the first column, the X-Y stage is moved along the direction opposite to the Y-axis direction while it is also moved along the X-axis direction to thereafter write a pattern in the unit area (2, 1). Similar to the operation sequence of writing patterns in the unit areas of the first column, patterns are written in the unit areas of the second column. Similarly, patterns are thereafter written in unit areas of the third to following columns.
The position accuracy of the X-Y stage moved by the above-described operation sequence was evaluated. Evaluation points (patterns) were disposed in a 15×15 matrix in a pitch 8.75 mm both in the X- and Y-axis directions, in a square area of 122.5 mm×122.5 mm of a plane of the X-Y stage. Of the evaluation points disposed in the matrix pattern, the evaluation points disposed along the column direction are given sequential numbers starting from the leftmost column, and the evaluation points disposed along the row direction are given sequential numbers starting from the lowest row. An evaluation point at the i-column and i-row is represented by P(i, j). This evaluation model corresponds to the case that unit areas are disposed in a matrix pattern of 15 rows×15 columns.
FIG. 5
is a diagram illustrating a displacement pattern of evaluation points. The horizontal direction in
FIG. 5
corresponds to the X-axis and the vertical direction corresponds to the Y-axis direction. The positive direction of the X-axis is rightward in
FIG. 5
, and the positive direction of the Y-axis is upward. The evaluation point P (1, 1) at the lowest left is moved to a reference point to detect a displacement amount between the evaluation point P (1, 1) and reference point. Next, a displacement amount at each evaluation point is detected while the evaluation point to be positioned at the reference point is sequentially moved along the positive Y-axis direction (while the X-Y stage is moved along the negative Y-axis direction).
After the evaluation point P (i, 15) at the uppermost row reaches the reference point, the target measurement position is moved along the positive X-axis direction by one column and along the negative Y-axis direction (the X-Y stage moves along the negative X-axis direction and along the positive Y-axis direction) until the evaluation point P (i+1, 1) at the lowest row reaches the reference point. Thereafter, the displacement amount at each evaluation point is detected sequentially from the evaluation point P (i+1, 1) at the lowest row to the evaluation point P (i+1, 15) at the uppermost row. This operation sequence is repeated until the displacement amounts at all evaluation points are detected.
In the example shown in
FIG. 5
, the pattern positioning accuracy was 53 nm (3&sgr;) in the X-axis direction and 44 nm (3&sgr;) in the Y-axis direction. Especially, it can be seen that the displacement amounts become large at the evaluation points P (i. 1) at the lowest row (start points in the positive Y-axis direction). This may be ascribed to that the motion style of the X-Y stage is different between the start points P (i, 1) and other evaluation points. In other words, the evaluation points (start points) reach the reference point while the X-Y stage moves obliquely upper left, whereas the other evaluation points (other than the start points) reach the reference point while the X-Y stage moves straight down.
In order to reduce the displacement amount at the start point, an X-Y stage approach running method has been proposed by which the X-Y stage moves toward the reference point from a position apart from some distance along the positive Y-axis direction where the start point P (i, 1) positions. With this method, the evaluation points (start points) also reach the reference point while the X-Y stage moves straight down.
FIG. 6
is a diagram showing a placement accuracy of evaluation points when the X-Y stage approach running method is shown. The approach running distance was set to 8.75 mm same as the pitch of evaluation points. The approach running distance is a distance to the start point from a point where the X-Y stage motion direction along the Y-axis direction is reversed. It can be seen that the displacement amounts at the start points are reduced when the approach running method is used more than when it is not used. The pattern positioning accuracy is 27 nm (3&sgr;) in the X-axis direction and 35 nm (3&sgr;) in the Y-axis direction, especially, which were improved more than those shown in FIG.
5
.
In the reticle production, all unit areas are not always disposed in a correct matrix pattern, nor Y-coordinate values of all start points are coincident.
FIG. 7
is a diagram showing an example of displacements when unit areas are not disposed in a correct matrix pattern. Evaluation points P (i, j) are disposed in a 13×13 matrix pattern, and the pitch of the evaluation points is 8.75 mm in both the X- and Y-axis directions. In order to disturb the regularity of motion of the X-Y stage, twelve pass points Q (m, n) (m=1, 2, 3, 4, n=1, 2, 3) indicated by black circles in
FIG. 7
are disposed. The pass points Q (m, n) are disposed at positions where evaluation points P (4m−3, 4n−2) are displaced by a half pitch along the negative X-axis direction.
First, the X-Y stage is moved so that the pass points Q (1, 1), Q (1, 2) and Q (1, 3) are sequentially positioned at the reference point. After the pass point Q (1, 3) reaches the reference point, the evaluation point P (1, 1) is moved to the reference point by using the X-Y state approach running method. A motion of the X-Y stage between the columns where the pass points are not disposed, is similar to the method described with FIG.
6
.
In the following, the motion from a column to another column, between which columns the pass points are disposed, e.g., the motion from the 4n-column to the (4n+1)-column, will be described. After the evaluation point P (4n, 13) is moved to the reference point, the pass points Q (n+1, 1), Q (n+
1
,
2
) and Q (n+1, 3) are sequentially moved to the reference point. Therea
Armstrong Westerman & Hattori, LLP
Fujitsu Limited
Wilson Lee D.
LandOfFree
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