Lithography system and method for processing a target, such as a wafer

Abstract

A method for operating a target processing system for processing a target (23) on a chuck (13), the method comprising providing at least a first chuck position mark (27) and a second chuck position mark (28) on the chuck (13); providing an alignment sensing system (17) arranged for detecting the first and second chuck position marks (27, 28), the alignment sensing system (17) comprising at least a first alignment sensor (61) and a second alignment sensor (62); moving the chuck (13) to a first position based on at least one measurement of the alignment sensing system (17); and measuring at least one value related to the first position of the chuck.

Description

TargetCenterToFirstSensor in measurement system coordinates. Next, the chuck 13 with the reference target 80 is positioned so that the center of the target is aligned under a second alignment sensor, e.g. alignment sensor 62. This second chuck position is measured and a second vector describing the second position is derived, e.g. vector [x, y]TargetCenterToSecondSensor in measurement system coordinates. These vectors establish the position of center of the reference target in relation to the alignment sensors.

This calibration is preferably performed once after any replacement or adjustment of the final projection system 11 or any of its components. The reference target is removed from the chuck 13 and a target to be processed is loaded on the chuck 13.

Alignment of the chuck to the calibrated mechanical scan direction may also be performed. After the chuck initialization procedure, the chuck 13 orientation still has no direct relation to either the alignment of the patterning beam 18 produced by final projection system 11 (i.e. the beam grid 60) or the alignment of the target 23 positioned on the chuck 13.

The chuck 13 is moved so that the beam 18 falls onto the beam measurement sensor 20, as depicted in FIG. 12A. Where the beam 18 comprises multiple sub-beams, a measurement of separation distance between sub-beams may be performed. For this measurement, the grid of sub-beams is swept across the blocking structure of the beam measurement sensor 20, and the resulting intensity values may be used to determine e.g. the distance between sub-beams, an average sub-beam to neighbouring sub-beam stitch vector, the size of the beam grid, and the orientation of the beam grid, in measurement system coordinates. This calibration may be performed once after each projection lens integration, or when the initialization position has become invalid, e.g. after a chuck swap or interferometer reintegration.

Next, the chuck 13 may be rotated in the Rz direction so that the y-axis of the chuck, which was previously determined during initialization, is aligned to a calibrated y-axis of the beam grid 60, as depicted in FIG. 12B. The current chuck 13 position now equals [x, y, z, Rx, Ry, Rz]_init−[0,0, 0, 0, 0, Rz]_BeamGrid. This enables a movement of the chuck in the y direction of measurement system coordinates to produce a movement along the intended mechanical scan direction, e.g. so that patterns written by neighboring beams stitch correctly to each other.

After loading target 23 onto chuck 13, the chuck is put in such orientation that the target surface (average or center) is aligned to the focal plane of the patterning beam 18, and the y-axis of the target layout is aligned to the y-axis of the beam grid. These [Rx,Ry,Rz] measurement system coordinates are used for all alignment sensor and beam position sensor measurements.

From the moment of the first until the last measurement with the alignment sensors during the expose scenario, it is important that the beam grid to alignment sensor vector remains identical. This requires that the mechanical stability of the alignment sensors to the beam grid axis remains stable. Therefore the alignment sensors are mounted in a ‘low expansion ring’.

The first step of the global alignment is the tilt measurement. The tilt of the target surface with respect to the level sensor plane is measured, and then the chuck is positioned so that the target surface at the center is aligned to the focal plane of the projection lens. One method for accomplishing this is by performing in the following steps, illustrated in FIGS. 13A and 13B. It will be understood that some of the steps described herein may be performed in different order and some steps combined into a single step (e.g. omitting intermediate chuck movements) without altering the end result, for all parts of the alignment procedure.

The chuck 13 is moved in the x- and y-directions as necessary to position the origin 29 of the chuck 13 under the origin 64 of the beam grid 60, as depicted in FIG. 13A. The chuck is also moved in the z-direction as necessary to position the origin 29 of the chuck in the focal plane of the final projection system 11. The origin 29 of the chuck has a fixed spatial relationship to the reference plate alignment marks 27, 28 and surface 26. The chuck initialization procedure enables the interferometer system to measure the position of the chuck 13 with respect to the beam grid 60, so that the origin 29 of the chuck can be aligned with the origin 64 of the beam grid 60.

The chuck 13 is rotated in the Rx- and Ry-directions as necessary to align the reference plate surface 26 in the level sensor plane, as depicted in FIG. 13B, and the chuck is further rotated in the Rz-direction to align the y-axis of the chuck 13 to the y-axis of the beam grid 60. This are the same Rx, Ry and Rz positions as at the end of the chuck initialization, e.g. [0, 0, 0, Rx, Ry, Rz]_init−[0, 0, 0, 0, 0, Rz]_yBeamGrid. In this chuck position, the level of target surface 12 is measured with the alignment level sensors 57, 58. This measurement is with respect to the level sensor plane.

The level sensing system 19 may be calibrated so that the level sensor plane nominally coincides with the focal plane of the patterning beam 18. There may nevertheless be small deviations between the two planes which may be taken care during calibration. Using the calibration settings, the chuck 13 is rotated in the Rx and Ry directions as necessary to align the target surface to the focal plane of the final projection system 11.

The next step is to align the chuck so that the target layout is aligned to the y-axis of the beam grid, and to determine the position of the origin of the target. This involves a global alignment in x, y and Rz-directions. One method for accomplishing this is by performing in the following steps, illustrated in FIGS. 14A-14E.

At this point a movement along the y-axis of the measurement system coordinates is nominally equal to movement along the mechanical scan direction, but eventually the y-axis of the target layout must be aligned to the beam grid. This alignment takes place during the global alignment after the target is loaded into the tool.

The chuck 13 is moved over the distance [x, y]TargetCenterToSecondSensor to position the center of the target under the first alignment sensor, e.g. alignment sensor 61, as depicted in FIG. 14A.

Before loading the target, the wafer load system measures the offset of the target position with respect to a ‘nominal’ target position. The center of the reference target is known, but the position of the center of the target to be patterned may vary slightly from the known value. The wafer load system may report how much offset there is from the reference target load. This may be done using a camera to pinpoint the target position marks when the target is loaded on the chuck in the wafer load system.

This offset plus the target coordinates of the target position marks on the target are used to calculate the scan parameters of the target position marks. The scan parameters typically include start and end positions and scan speed of a step movement. The chuck is moved to position each x-axis target position mark 76 under the first alignment sensor 61 and the actual position of the x-axis target position marks with respect to the beam gird is measured, as depicted in FIG. 14B.

The chuck 13 is next moved over the distance [x, y]TargetCenterTargetToFirstSensor to position the center of the target under the second alignment sensor, e.g. alignment sensor 62, as depicted in FIG. 14C. The chuck is moved to position each y-axis target position mark 77 under the second alignment sensor 62 and the actual position of the y-axis target position marks with respect to the beam gird is measured, as depicted in FIG. 14D.

The rotation of the target layout in the Rz direction is calculated with respect to the beam grid in measurement system coordinates. The chuck 13 is rotated in the Rz-direction by the calculated amount to align the target layout coordinates to the y-axis of the beam grid, as depicted in FIG. 14E.

Together with the rotation of the target in measurement system coordinates, the shift of the target in measurement system coordinates can be calculated. This results in the transformation between target and measurement system coordinates, which can be expressed as a transformation matrix:

${\left[\begin{array}{c}x\\ y\end{array}\right]}^{\mathrm{MES}}={\underset{\underset{{\sum }_{\mathrm{Global}}^{\mathrm{Wafer}->\mathrm{MES\_ALS}}}{︶}}{{\left[\begin{array}{c}{T}_x^{\mathrm{Wafer}}\\ T_y^{\mathrm{Wafer}}\end{array}\right]}^{\mathrm{MES}}+\left[\begin{array}{cc}1& -R^{\mathrm{Wafer}}+R_a^{\mathrm{Wafer}}\\ R^{\mathrm{Rafer}}+R_a^{\mathrm{Wafer}}& 1\end{array}\right]}\left[\begin{array}{c}x\\ y\end{array}\right]}^{\mathrm{Wafer}}$

where T is a 2×1 translation vector describing the position of the origin of the target in measurement system coordinates, and R is a 2×2 rotation matrix describing the orientation of each of the axis (x and y axes) of the target in measurement system coordinates. The transformation describes the offset of the wafer in measurement system coordinates to have a first target position mark aligned to a first alignment sensor and a second target position mark aligned to a second alignment sensor.

FIG. 15 shows a schematic overview of a lithography system according to an embodiment of the invention, which may comprise elements of a lithography system as described herein. The lithography system is preferably designed in a modular fashion to permit ease of maintenance. Major subsystems are preferably constructed in self-contained and removable modules, so that they can be removed from the lithography machine with as little disturbance to other subsystems as possible. This is particularly advantageous for a lithography machine enclosed in a vacuum chamber, where access to the machine is limited. Thus, a faulty subsystem can be removed and replaced quickly, without unnecessarily disconnecting or disturbing other systems.

In the embodiment shown in FIG. 15 these modular subsystems include an illumination optics module 801 which may comprise a beam source 802 and beam collimating system 803, an aperture array and condenser lens module 804 including aperture array 805 and condenser lens array 806, a beam switching module 807 including sub-beam blanker array 808, and projection optics module 809 including beam stop array 810, beam deflector array 811, and projection lens arrays 812. The above-mentioned final projection system may refer to the projection lens arrays 812.

The modules may be designed to slide in and out from an alignment frame. In the embodiment shown in FIG. 15, the alignment frame may comprise an alignment inner sub frame 813 and an alignment outer sub frame 814. In the above flexures have been described for connecting the final projection system with a frame 71. In FIG. 15, this connection and thus the flexures are not shown. However, the frame 71 may correspond to the alignment inner sub frame 813 or the alignment outer sub frame 814. A main frame 815 may support the alignment subframes 813 and 814 via vibration damping mounts 816. The wafer or target rests on wafer table 817, which is in turn mounted on chuck 13.

For simplicity, the wafer table 817 has not been mentioned in the above description. Chuck 13 sits on the stage short stroke 818 and long stroke 819. The stage short stroke 818 and long stroke 819 may comprise the actuator system described above. The lithography machine may be enclosed in vacuum chamber 820, which may include a mu metal shielding layer or layers 821. The system may rest on base plate 822 and may be supported by frame members 823.

The various module typically require a large number of electrical signals and/or optical signals, and electrical power to operate the module. The modules inside the vacuum chamber may receive these signals from a processor unit 824 which is typically located outside of the chamber.

The patterning beam may be collimated by collimator lens system 803. The collimated beam impinges on an aperture array 805, which blocks part of the beam to create a plurality of sub-beams. The lithography system is preferably arranged for generating a large number of sub-beams, preferably about 10,000 to 1,000,000 sub-beams. The sub-beams may pass through a condenser lens array 806 which may focus the sub-beams in the plane of a beam blanker array 808, comprising a plurality of blankers for deflecting one or more of the sub-beams. The deflected and undeflected sub-beams may arrive at beam stop array 810, which may have a plurality of apertures. The sub-beam blanker array 808 and beam stop array 810 may operate together to block or let pass the sub-beams. If sub-beam blanker array 808 deflects a sub-beam, it will not pass through a corresponding aperture in beam stop array 810, but instead will be blocked. But if sub-beam blanker array 808 does not deflect a sub-beam, then it will pass through the corresponding aperture in beam stop array 810, and through beam deflector array 811 and projection lens arrays 812.

The beam deflector array 811 may provide for deflection of each sub-beam in the x and/or y direction, substantially perpendicular to the direction of the undeflected sub-beams, to scan the sub-beams across the surface of the target. The sub-beams may pass through projection lens arrays 812 and may be projected onto the target. The projection lens arrays 812 preferably provide a demagnification in the order of to 500 times (depending of the specific electron-optical lay out). The sub-beams may impinge on the surface of target positioned on moveable chuck 13 for carrying the target.

For lithography applications, the target usually is a wafer provided with a charged-particle sensitive layer or resist layer. The lithography system may operate in a vacuum environment. A vacuum may be desired to remove particles which may be ionized by the beams and become attracted to the source, may dissociate and be deposited onto the machine components, and may disperse the beams. In order to maintain the vacuum environment, the lithography system may be located in a vacuum chamber. All of the major elements of the lithography system are preferably housed in a common vacuum chamber, including the beam source, the optical column and the moveable chuck.

It may be understood that the described embodiment of a lithography system using an electron beam to pattern a target may also be applied to a lithography system using a light beam to pattern a target, mutatis mutandis. It is to be understood that the above description is included to illustrate the operation of the preferred embodiments and is not meant to limit the scope of the invention. From the above discussion, many variations will be apparent to a person skilled in the art that are encompassed by the appended claims and are within spirit and scope of the present invention.

Claims

1. A method for operating a target processing system for processing a target on a chuck, the method comprising:

providing at least a first chuck position mark and a second chuck position mark on the chuck;

providing an alignment sensing system comprising at least a first alignment sensor and a second alignment sensor arranged for detecting the first and second chuck position marks respectively;

providing a chuck position measurement system comprising at least two differential interferometers arranged to measure the position of the chuck with respect to a final projection system of said target processing system;

providing a level sensing system comprising a plurality of level sensors, and providing a reference surface on the chuck;

moving the chuck to a first position based on at least one measurement of the alignment sensing system, said moving the chuck comprising moving the chuck to align the first and second chuck position marks with the first and second alignment sensors and reading the first and second chuck position marks by the first and second alignment sensor;

measuring at least one value relating to the orientation of the reference surface with respect to the level sensors, and moving the chuck to align the reference surface with a level sensor plane of the plurality of level sensors, such that in the first position the first and second chuck position marks are aligned with the first and second alignment sensors and the reference surface is aligned with the level sensor plane;

measuring at least one value related to the first position of the chuck, wherein measuring at least one value related to the first position of the chuck comprises measuring an output of each of the differential interferometers; and

initializing each of the differential interferometers with the chuck located at the first position, based on said measuring of said at least one value related to the first position of the chuck.

2. The method of claim 1, wherein the relative position of the first chuck position mark with respect to the second chuck position mark is substantially the same as the relative position of the first alignment sensor with respect to the second alignment sensor.

3. The method of claim 1, further comprising providing a final projection system arranged to project a patterning beam onto the target, and wherein the first alignment sensor is arranged at a distance from the final projection system in a first direction (y-axis) and the second alignment sensor is arranged at distance from the final projection system in a second direction (x-axis).

4. The method of claim 1, further comprising projecting a patterning beam onto the target to form a beam grid on the target, wherein the first alignment sensor is arranged for detecting a position mark at a distance from the beam grid in a first direction (y-axis) and the second alignment sensor is arranged for detecting a position mark at a distance from the beam grid in a second direction (x-axis).

5. The method of claim 1, wherein the step of moving the chuck to align the chuck position marks with the alignment sensors comprises moving the chuck in two horizontal axes (x, y-axis) and rotating the chuck about a vertical axis (Rz direction) as necessary to achieve the alignment.

6. The method of claim 1, further comprising moving the chuck to align the reference surface with a level sensor plane of the level sensors prior to measuring at least one value relating to orientation of the beam grid.

7. The method of claim 1, wherein the level sensing system comprises at least a first level sensor arranged at a distance from the final projection system in a first direction (y-axis) and a second level sensor arranged at distance from the final projection system in a second direction (x-axis).

8. A target processing system for processing a target on a chuck, the system comprising:

a moveable chuck including at least a first chuck position mark and a second chuck position mark;

an alignment sensing system comprising at least a first alignment sensor and a second alignment sensor arranged for detecting the first and second chuck position marks respectively,

a level sensing system comprising a plurality of level sensors, and a reference surface on the chuck, said level sensing system arranged for measuring at least one value relating to the orientation of the reference surface with respect to the level sensors;

an actuator system arranged for moving the chuck;

a chuck position measurement system arranged for measuring a position of the chuck, the chuck position measurement system comprising at least two differential interferometers arranged to measure the position of the chuck with respect to a final projection system of said target processing apparatus,

9. The system of claim 8, wherein the relative position of the first chuck position mark with respect to the second chuck position mark is substantially the same as the relative position of the first alignment sensor with respect to the second alignment sensor.

10. The system of claim 8, further comprising a final projection system arranged to project a patterning beam onto the target, and wherein the first alignment sensor is arranged at a distance from the final projection system in a first direction (y-axis) and the second alignment sensor is arranged at distance from the final projection system in a second direction (x-axis).

11. The system of claim 8, further comprising a final projection system for projecting a patterning beam onto the target to form a beam grid on the target, wherein the first alignment sensor is arranged for detecting a position mark at a distance from the beam grid in a first direction (y-axis) and the second alignment sensor is arranged for detecting a position mark at a distance from the beam grid in a second direction (x-axis).

12. The system of claim 8, wherein, the measurement system is arranged for measuring at least one value related to the current position of the chuck.

13. The system of claim 8, further comprising a final projection system arranged to project a patterning beam onto the target, wherein the level sensing system comprises at least a first level sensor arranged at a distance from the final projection system in a first direction and a second level sensor arranged at distance from the final projection system in a second direction (x-axis).

14. A target processing system for processing a target on a chuck, the system comprising:

a final projection system arranged to project a patterning beam plurality of charged particle beams onto the target to form a beam grid on the target;

a moveable chuck including at least a first chuck position mark and a second chuck position mark provided on a surface of said chuck;

an actuator system arranged for moving the chuck;

an alignment sensing system comprising at least a first alignment sensor and a second alignment sensor arranged for detecting the first and second chuck position marks respectively,

a level sensing system comprising a plurality of level sensors arranged on a bottom surface of the final projection system in close proximity to the beam grid and in a fixed spatial relation to the final projection system;

a reference surface provided on a surface of said chuck, said level sensing system arranged for measuring at least one value relating to distance and/or orientation of the reference surface with respect to said level sensors;

a chuck position measurement system arranged for measuring a position of the chuck, the chuck position measurement system comprising at least two differential interferometers arranged to measure the position of the chuck with respect to the final projection system of said target processing apparatus.

15. The target processing system according to claim 14, wherein the chuck is provided with a reference plate comprising the reference surface and the first and second chuck position marks.

16. The target processing system according to claim 14, wherein an origin of the chuck has a fixed spatial relationship to the first and second chuck position marks and the reference surface.

17. The system of claim 14, wherein the level sensing system further comprises a second plurality of level sensors, wherein the first alignment sensor and a first of said second plurality of level sensors are arranged at a distance from the final projection system in a first direction and the second alignment sensor and a second of said second plurality of level sensors are arranged at distance from the final projection system in a second direction.

18. A target processing system for processing a target on a chuck, the system comprising:

a moveable chuck including at least a first chuck position mark and a second chuck position mark;

an alignment sensing system arranged for detecting the first and second chuck position marks respectively;

a level sensing system comprising a plurality of level sensors, and a reference surface on the chuck, said level sensing system arranged for measuring at least one value relating to the orientation of the reference surface with respect to the level sensors;

an actuator system arranged for moving the chuck; and

a chuck position measurement system arranged for measuring a position of the chuck, the chuck position measurement system comprising at least two interferometers arranged to measure the position of the chuck with respect to a final projection system of said target processing apparatus,

wherein said target processing system is configured to initialize said interferometers by: using said actuator system to move the chuck to align the first and second chuck position marks with the alignment sensing system, while the first and second chuck position marks are read by the alignment sensing system and the chuck is moved such that the reference surface coincides with a level sensor plane,

wherein the position where the first and second chuck position marks are aligned with the alignment sensing system, and the reference surface on the chuck coincides with the level sensor plane is referred to as a first position of the chuck, wherein said chuck position measurement system is configured to measure at least one value related to the first position of the chuck, and wherein said measurement of said at least one value related to the first position of the chuck comprises a measurement of an output of the interferometers and an initialization of the interferometers with the chuck located at the first position based on said measurement of said at least one value related to the first position of the chuck.

19. A target processing system for processing a target on a chuck, the system comprising:

a projection system configured to project a plurality of charged particle beams onto the target to form a beam grid on the target;

a moveable chuck including at least a first chuck position mark and a second chuck position mark provided on a surface of the chuck;

an actuator system configured to move the chuck;

an alignment sensing system comprising at least a first alignment sensor and a second alignment sensor configured to detect the first and second chuck position marks;

a level sensing system comprising a plurality of level sensors having a fixed spatial relationship with the projection system;

a reference surface provided on the chuck, the level sensing system configured to measure at least one value relating to distance and/or orientation of the reference surface with respect to the level sensors;

a chuck position measurement system configured to measure a position of the chuck, the chuck position measurement system comprising at least two interferometers configured to measure the position of the chuck with respect to the projection system; and

a beam measurement unit provided on the chuck and configured to detect the charged particle beams to determine positions of the charged particle beams relative to the chuck.

20. The target processing system according to claim 19, wherein the plurality of level sensors are provided on a bottom surface of the projection system.

21. The target processing system according to claim 19, wherein the at least two interferometers are configured to measure the position of the chuck in at least two different respective directions in a plane across the charged particle beams.

22. The target processing system according to claim 19, further comprising a vacuum chamber comprising the projection system, the chuck, the actuator system, the alignment sensing system, the level sensing system, the chuck position measurement system, and the beam measurement unit.

23. The target processing system according to claim 19, wherein the beam measurement unit includes a beam measurement sensor comprising chuck position marks.

24. The target processing system according to claim 19, wherein the beam measurement unit includes a beam measurement sensor comprising a two-dimensional pattern of charged particle beam blocking structures.

25. The target processing system according to claim 23, wherein the beam measurement sensor comprises a two-dimensional pattern of charged particle beam blocking structures, the pattern having a pre-determined spatial relationship with the chuck position marks.

26. The target processing system according to claim 23, wherein the chuck position marks are arranged in at least two different directions.

27. The target processing system according to claim 26, wherein the chuck position marks are configured as gratings.