Radiant energy – Photocells; circuits and apparatus – With circuit for evaluating a web – strand – strip – or sheet
Reexamination Certificate
2001-11-15
2004-07-06
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
With circuit for evaluating a web, strand, strip, or sheet
C250S559300
Reexamination Certificate
active
06759670
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for dynamic manipulation and for adjustment of a module or a component in an optical system in the sub-&mgr;m range. More specific the invention relates to a method for dynamic manipulation and for adjustment of a module or a component in a microlithographic projection, exposure objective in the sub-&mgr;m range for the manufacture of semi-conductors.
2. Description of the Related Art
In order to adjust modules or components in optical systems in the sub-&mgr;m range, the general prior art knows only very elaborate adjustment processes, which need to be carried out “by hand” by experienced persons skilled in the art. To that end, use is made of control elements provided with corresponding step-up or step-down transmissions, for example with screw or worm drives or the like.
It is also known to persons skilled in the art that very fine re-adjustments of the components are possible through vibrations or impulses which, for example, can be applied to the corresponding components by means of a small hammer.
DE 42 36 795 C1 describes a corresponding device for adjusting mechanical components. The displacement of the components needed for the adjustment, this special case being one which relates to mirrors, is brought about using a mechanical pulse generator which, by means of a striker pin, exerts an impulse on the mounting of the component to be adjusted in a manner comparable with the aforementioned hammer.
This setup described in the aforementioned document is also comparatively elaborate, since it requires correspondingly high forces in order to be able to shift the components against their clamping, which is intended to hold them by a frictional lock.
In this method, vibrations also occur in the optical system, which can very easily lead to de-adjustment of components in a neighboring region.
The fact that owing to the vibrations, the optical quality of desired imagings cannot be ensured, at least at the time of the applied impulse, must certainly be regarded as a further disadvantage of the device described by the aforementioned document. The device is therefore unsuitable for dynamic manipulations, i.e. in general controlled re-setting during operation of the optical system.
Per se conceivable manipulation or adjustment by continuous movement of the components cannot, however, also be achieved in the sub-&mgr;m range since, in this case, effects due to unavoidable mechanical roughnesses and inaccuracies occur, which lead to serious problems and undesired positional changes of the components. For instance, the inventors' experience has shown that with all conventional control methods, which operate with proportional and/or integral and/or differential control aspects, satisfactory results cannot be achieved for the positioning of components in accuracy ranges of a few nanometers. This is probably due to the aforementioned mechanical inaccuracies which are reflected, for example, in microroughnesses, very nonuniform slip-stick effects and slight deviations of the mechanical components, for example the stiffnesses of solid-state joints or the like.
SUMMARY OF THE INVENTION
It is therefore the object of the invention to provide a method which, in particular, permits dynamic manipulation of the corresponding components, but also adjustment of the components, and which, with very few method steps, is capable of displacing the corresponding components in the sub-&mgr;m range into a sufficiently accurate position.
According to one aspect of the invention, this object is achieved by a method for dynamic manipulation of a module or a component in an optical system in the sub-&mgr;m range, the module or component being displaced by at least two actuators, which have detectors for determining at least their relative path displacements, a position of the module or component being determined by at least two sensors, the sensors and the actuators with their detectors communicating with one another in the manner of a control loop, and at least one mechanical impulse being exerted on the module or component by the actuators, wherein the timing of the impulse can be deliberately varied, to which end the displacement of the actuators is carried out with a time-variant velocity profile dictated as a function of a determined position (s
n
actual
) with respect to a setpoint position (s
setpoint
) of the module or component, the said position (s
n
actual
) of the module or component being re-determined after the velocity profile has been executed, and the aforementioned method steps being repeated until the desired position (s
setpoint
) of the module or component is reached.
In this context, the inventors have surprisingly and unexpectedly found that by the two consecutively organized method steps, in which the actuators execute the velocity profile and then, depending on the determined actual position, execute a further velocity profile matched to the setpoint/actual difference, it is possible to position the components very rapidly, i.e. with few repetitions of these steps.
It has been shown in tests that positioning with from three to at most five method steps is entirely realistic, which offers the particular advantage that this method is very fast and is therefore suitable for dynamic manipulation, i.e. re-adjustment of the microlithographic projection exposure objective of the modules or component during operation of the optical system.
In contrast to the problems, mentioned in the introduction, with the conventional control methods (PID controllers), the method according to invention provides both faster and better and more reliable manipulation of the optical elements.
The known problems of microlithographic projection exposure objectiveing in the sub-&mgr;m range, which are due to microroughnesses, slip-stick effects and slight deviations of the mechanical components, for example the stiffnesses of solid-state joints or the like, can be compensated for in a particularly favorable manner by the method according to the invention, which virtually enables an iterative approximation of the actual microlithographic projection exposure objective to the desired setpoint microlithographic projection exposure objective of the component or module.
It should fundamentally be pointed out that at least the rough relationship between the specified setpoint values and the actual value, which can never be exactly achieved owing to the aforementioned errors, should be of a linear form. The real function of the relationship will certainly be a very “wild” and unsteady curve, albeit one which can be approximated at least very roughly by the aforementioned linear relationship. Now, if the positioning steps to be achieved, which are reached through the variable velocity profile with which the actuators are driven, are rough enough, then the values will be oriented along this specified slope, so that the individual points that are actually achieved on the unsteady setpoint/actual function curve approximate the desired setpoint value in the manner of an iteration.
In a particularly favorable embodiment of the aforementioned method, it is in this case very favorable for the velocity profiles to respectively have at least one velocity gradient rising from an initial velocity and one velocity gradient falling to a final velocity, the slopes of which are matched in accordance with the path section still to be traveled, which in general becomes smaller and smaller from one method step to the next. For very large path sections, this may be a comparatively gently rising velocity gradient, which is followed by a further flat or optionally even constant velocity, before the corresponding final velocity is reached through a falling velocity gradient. If only very small positioning steps are needed, then it is possible for an only very small impulse, which then correspondingly entails only a very small displacement, to be given to the actuators through a very steep rising velocity gradient and a velocity gradient falling very st
Le Que T.
Welsh & Katz Ltd.
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