This application claims priority to German patent application number DE 10 2004 058 967.4-51, filed Dec. 8, 2004, which is incorporated herein by reference in its entirety.
The invention relates to exposing on a substrate with a beam.
In SB3xx systems from Leica Lithography GmbH, the maximum possible constant table speed is calculated for each exposure strip by simulating the exposure cycle in advance.
The importance of speed in this mode is made clear by publication JP08/236,420AA. Strip width is determined in advance such that a minimum or maximum speed is neither over- nor undershot. However, adjusting the speed to the density of the image contents is not considered.
Publication JP000006196394AA also describes the interplay between various articulation systems that make possible continuous table movement. However, the speed is intentionally kept constant.
The solution described in JP000006151287AA takes into account the varying density of image contents in so far as parts are to be exposed repeatedly at longer exposure times. However, this is only meant to ensure that the exposure process can follow the table movement without having to take into account the time required for twice positioning on one and the same substrate.
The object underlying the invention is to create a method for exposing on a substrate with a beam, by which the throughput is increased when exposing the substrate.
This object is solved by a device with the characteristics in claim 1.
The method is advantageous because the speed of the substrate carrier system can be adjusted during exposure depending on the density of the exposure pattern. The substrate carrier system defines a track curve, whereby the exposure pattern is exposed within a band around the track curve.
The beam system comprises a primary deflector system and a micro deflector system, whereby the primary deflector system pre-positions the beam on the individual partial working field within the track curve in order to produce the exposure pattern there. The track curve is a strip on the substrate that exhibits a surface that is smaller than that of the substrate itself.
The change in speed at which the track curve is defined is first determined based on the density of the exposure pattern, dependent on parameters of the substrate carrier system and parameters of the beam system. The beam system parameters comprise the response times and deflection ranges of the deflection system and the overhead time of the electronic control mechanism.
The lag time for correcting the position of the substrate carrier system and of the beam system to ensure precise positioning of the exposure pattern on the substrate is determined based on the local speed of the substrate carrier system.
The beam system exhibits a primary deflector system and a micro deflector system, whereby the primary deflector system pre-positions the beam on the individual partial working field within the track curve in order to produce the exposure pattern there. The track curve forms a strip on the substrate that exhibits a surface that is smaller than that of the substrate itself.
The change in speed at which the track curve is defined is first determined based on the density of the exposure pattern, dependent on parameters of the substrate carrier system and parameters of the beam system. The beam system parameters comprise the maximum permissible acceleration and the minimum and maximum speed of the substrate carrier system. The parameters of the beam system comprise the response times and deflection ranges of the deflection systems and the overhead time of the electronic control system.
The lag time for correcting the position of the substrate carrier system and of the beam system to ensure precise positioning of the exposure pattern on the substrate is determined based on the local speed of the substrate carrier system.
Further advantageous developments of the invention may be found in the subclaims.
The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.
In the accompanying drawings, reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale; emphasis has instead been placed upon illustrating the principles of the invention. Of the drawings:
The diagrams show schematically the object according to the invention, which will be described below on the basis of the figures. They show:
An electron cannon 30 generates an electron beam 31 that spreads out in the direction of an electron optical axis 32. The electrons emitted by the electron cannon 30 exhibit a source crossover 31. The electron cannon 30 is connected to a beam centering device 33 that aligns the electron beam 31 symmetrically around the optical axis 32. After the beam centering device, the electron beam 31 passes through an illumination condenser 10, which forms a parallel beam from the initially divergent electron beam. A beam forming system 35 is provided in the direction of spread of the electron beam 35 toward a substrate 6. Furthermore, the system comprises a primary deflector system 25 and a micro deflector system 23, whereby the primary deflector system 25 pre-positions the beam within the track curve (see
In the very simplified exemplary schematic representation (see
All operations that are depicted and others required for the exposure cycle (adjusting the beam form and imaging sharpness: intermediate adjustments for height correction, etc.) required time, during which the table 51 continues to move. Tracking by means of the primary deflection system 25 with the table that has just been described, is only possible within certain limits, which in
Because the time needed for fixing the system and processing parameters to be used while exposing of the exposure pattern within a band 60 around a track curve 621, 622, . . . 62n (for more, see
A mathematical model (embodiment of the invention) for controlling the speed can be described as follows:
[xA, xE] describe control intervals within which the speed is to be changed.
v(x), xε[xA, xE] Is the control function for table speed at Point X.
the average speed above [xA, xE] can be calculated using the formula herein.
The task is now to find the maximum speed at which the table or the substrate carrier system, respectively, may be moved. The speed is dependent on the exposure pattern that is to be written in each partial working field.
Maximization of throughput speed is determined by the above formula.
A series of secondary conditions determine the speed at which the substrate carrier system 50 can be moved.
The class of functions for the control function v(•) of the speed is determined by:
Performance and secondary conditions of a system with variable speed control:
The following characteristic features result:
t(•) is dependent on v(•) (additional resetting of the beam system, hold times at the right stop limit 62 of the primary deflection system 23)
t(•) can only be estimated (complexity of the actual interplays; indeterminate influences)
One possibility for solving this problem is to first establish a specialized target model. Then one must determine a preliminary solution for a suitable model relaxation. Iterations of the exposure simulation follow until an allowable solution for the target model is achieved.
Model relaxations for determining preliminary solutions can, for example, be obtained by allowing more general control functions v in comparison with the target model (e.g., a greater number and/or more freely positionable control points). By the same token, the use of local limit speeds instead of global feasibility conditions is also possible.
Examples of speed control according to this model are described in the following. The circumstances of drive motor control of this system do not permit continuous realization (such as in the sense of defining a curve) of a suitably calculated speed profile, but only permit the setting of a certain number of discrete control points xA=x0<x1< . . . <xn=xE for which a certain speed is to be achieved. This should not, however, be interpreted as a limitation of the invention. Whenever the drive motor control permits, continuous realization, i.e., continuous control of the speed, is also possible. The actual realized speed between these switch points cannot be changed; however, it is calculable with adequate precision, monotonically increasing or decreasing at increasing or decreasing speed from one control point to the next, and moreover monotonically evenly dependent on speeds in the control points (i.e., {overscore (v)}(xi-1)≦v(xi-1)ˆ{overscore (v)}(xi)≦v(xi){overscore (v)}(x)≦v(x)∀xε[xi-1, xi], analogous for “≧”).
Example 1 relates to control at a constant speed that is integrated in the model.
Model:
v(x)≡const
Relaxation:
The maximum speed possible in the densest partial working field 6a (high exposure pattern density) taking into account the secondary technical conditions (maximum table speed, permissible maximum number of additional resets of the beam tracker, etc.) yields the preliminary solution.
Iteration:
Simulation of the exposure process. The initial speed is decreased for as long as it takes to do the exposure.
Model:
The control points xA=x0<x1< . . . <xn=xE are preset and are all laid out on the columns and limits of the partial working field. These may, for example, have been determined in a preparatory step based on a preset control point minimum interval ax such that Δx≦xi−xi-1, i=1, . . . , n, applies. The maximum allowable change in speed for all segments Ai=[xi-1, xi] so defined by segment length ai=xi−xi-1, i=1, . . . n, is to be uniformly the same as Δv.
Relaxation:
The maximum speed in the densest partial working field 6a of each segment is determined (as in Example 1). The resulting speeds are v1, . . . , vn. If one then sets wi=v(xi), i=0, . . . , n, one then gets the following linear optimization problem for determining a piecewise monotonic preliminary solution v(•):
under secondary conditions
α) wi≦vi, wi-1<vi, i=1, . . . n,
β) |wi-1−wi|≦Δv, i=1, . . . n.
It is notable that the concrete form of v(•) between the control points have no influence on the optimization of a solution to this problem—in so far as the above-mentioned monotonic characteristics are met.
Iteration:
Simulation of the exposure cycle. If exposure is recognized as not being feasible, the speed in the current or previous segment is decreased, permissibility in the sense of relaxation is created, and a renewed iteration done. Criteria for the selection of the segment in which the speed is decreased result from the course of the iteration.
While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.
Number | Date | Country | Kind |
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DE102004058967.4- | Dec 2004 | DE | national |