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Patent Issued for Positioning Method for an Optical Arrangement of a Projection Illumination System

September 3, 2014



By a News Reporter-Staff News Editor at Journal of Engineering -- Carl Zeiss SMT GmbH (Oberkochen, DE) has been issued patent number 8810934, according to news reporting originating out of Alexandria, Virginia, by VerticalNews editors.

The patent's inventors are Aubele, Karl-Eugen (Geislingen/Steige, DE); Merz, Erich (Essingen, DE); Rassel, Thorsten (Huettlingen, DE).

This patent was filed on March 17, 2011 and was published online on August 19, 2014.

From the background information supplied by the inventors, news correspondents obtained the following quote: "Projection illumination systems are used for the microlithographic production of microelectronic devices, in particular semiconductor devices or devices for micro- and nanotechnology. In order to produce structures with very small dimensions, it is desirable to image the structures in the projection illumination system with a high degree of accuracy. Even the smallest changes in the optical elements used in the projection illumination system with respect to their form, composition or their position in the optical arrangement can result in corresponding aberrations and thus to defectiveness of the devices to be produced.

"Accordingly it is known to use methods for positioning and/or adjusting optical elements in optical arrangements of a projection illumination system, which methods conform to the highest desired properties in terms of the accuracy of the positioning. DE 102 25 266 A1, for example, describes an imaging apparatus of a projection illumination system for microlithography, in which manipulators with piezoactuators are used in order to manipulate and position relevant optical elements, such as for example optical lenses, mirrors or the like.

"The disclosure of DE 102 25 266 A1 and of U.S. Pat. No. 6,150,750, which describes piezoactuators in the form of linear piezo drives, are incorporated by reference herein in their entirety.

"Although a very exact positioning of optical elements is already possible with the linear piezo drives, as they are described in the previously mentioned documents, there is furthermore a desire for efficient operating methods which enable, in addition to simple and effective operation of the manipulators, at the same time extremely exact positioning with a high degree of accuracy.

"It has been shown that the fact that the movement of the linear piezo drives and/or the movement of the optical elements which are moved thereby or of the gear elements such as actuating levers or the like which are possibly provided between the optical element to be manipulated and the linear piezo drive is delimited by abutment elements results in interactions with the abutment element possibly resulting in influences on the optical element. When the abutment element comes into contact in the peripheral movement region of the manipulation apparatus, the optical element can be negatively affected with corresponding negative effects on the imaging properties. It is desirable for this reason to use a corresponding positioning method which takes into account these possible negative influences."

Supplementing the background information on this patent, VerticalNews reporters also obtained the inventors' summary information for this patent: "The disclosure seeks to provide a method for producing, setting and/or adjusting an optical arrangement, in particular for positioning an optical element in an optical arrangement of a projection illumination system, in which exact positioning is possible in a simple and effective manner by way of incremental movement of the optical element.

"In addition, a negative influence of abutment elements, which delimit the movement region, is intended to be avoided.

"The disclosure proceeds from the knowledge that for exact and effective positioning of an element in an optical arrangement of a projection illumination system, in the case of an incremental movement of the optical element by at least one (preferably more than one) actuator (such, as for, example piezoactuators, and preferably linear piezo drives), the problems described above can be solved in a simple manner by setting the increments and by detecting the deviation from a pre-specified increment size.

"Accordingly, according to a first aspect of the present disclosure, the incremental movement of the optical element is intended to be performed such that the increment size is set as a function of the distance of the optical element from the desired position, with the distance of the optical element from the desired position being represented by a distance value. This distance value can be given by a simple displacement value or by a displacement vector, which additionally gives the corresponding directions. In particular it is possible, however, preferably when using a simple one-dimensional displacement value as the distance value, that the disclosure (as will be described below for example for an individual linear piezo drive) is designed for a plurality of linear piezo drives at the same time, which linear piezo drives are responsible for the movement in different independent spatial directions, such as for example in the directions of the X-, Y- and Z-axes of a Cartesian coordinate system.

"According to the disclosure, the increment size for approaching the optical element to be manipulated from an instantaneous position to a desired position should initially be set as a constant increment size, for example the maximum increment size of the actuator, as long as the distance value is above a first threshold value. If the distance value is below the threshold value, the increment size is reduced in accordance with the decrease of the distance value. Owing to the first approaching movement with a constant, especially maximum, increment size up to a first threshold value, a fast approaching movement to the desired position can take place. Once the distance value falls below the first threshold value, the increment size is reduced in order to enable an exact approaching movement to the desired position. Exact positioning can be carried out by way of repeated performance of the corresponding approaching cycle with a check of whether the distance value is below or above the first threshold value, that is to say what the instantaneous position relative to the desired position is, and of a corresponding performance of the movement increments according to the result of the check.

"According to a further aspect of the present disclosure (which can be implemented itself and/or in conjunction with the first aspect of the disclosure noted above), a deviation of the increment size from the pre-specified increment size and/or the deviation of an increment size change rate from a pre-specified increment size change rate, that is to say the deviation of the movement velocity from a pre-specified movement velocity or the deviation of a movement acceleration or deceleration from a pre-specified movement acceleration or deceleration, is used as an indication of the optical element approaching an abutment element, such that either an appropriate warning signal can be emitted and/or the movement can be stopped. If the optical element is moved by the manipulators into the region of an abutment element, an additional movement of up to a size range of 0.5 .mu.m can take place due to appropriate matching processes after first contact of the optical element, or the actuator and gear devices that are connected in-between, before the final physical stop of the optical element occurs. However, negative effects on the optical element are assumed from the very first contact, and therefore this first contact can already be determined by the method according to the disclosure.

"Accordingly, this advantageous method can also be used independently of an actual positioning and/or adjustment of an optical element for ascertaining the movement region. In this case, the movement in the direction of the abutment element is performed with a pre-specified or maximum increment size until first contact can be ascertained on the basis of the deviation of the increment size or the increment size change rate from pre-specified values. In other words, with a pre-specified constant movement velocity, that is to say a constant increment size per movement increment, the deviation from this constant movement velocity outside a pre-specified acceptable range can be taken as an indication of a contact with the abutment element, such that this first contact point can already be used to determine the end of the movement region.

"In the method according to the disclosure for the production and/or adjustment of an optical arrangement of a projection illumination system, the movement increments can be performed repeatedly, wherein individual approaching cycles can contain a plurality of movement increments or individual movement increments. The approaching cycles can be performed repeatedly until the desired positioning is achieved.

"Moreover, a control loop and at least one position sensor, preferably a plurality of position sensors, in particular capacitive position sensors, can be provided, wherein a corresponding distance value can be ascertained by way of ascertaining the instantaneous position of the optical element to be manipulated using the position sensors and comparing it to the desired position, which distance value can in turn serve the control loop for the determination of the increment size in the next approaching cycle or in the next movement increment. Alternatively, the distance value can also be input directly, if no position sensors are available and the distance value can be ascertained by another mechanism.

"The first threshold value can be in particular be given by the maximum increment size of the actuator or actuators. Accordingly, it is possible, if a distance value is above this first threshold value, to always perform a movement increment with the maximum increment size of the actuator, without running the risk of going beyond the desired position.

"If a distance value is below this first threshold value, it is possible to perform a movement increment with a correspondingly reduced increment size as a function of the distance value.

"The positioning method according to the disclosure can be supplemented by determining a second threshold value that corresponds to a distance value which is greater than the first threshold value. If the distance value, which is input into the system or determined by the control loop or the position sensors, of the actual position of the optical element from the desired position is greater than the second threshold value, a first approaching movement can take place by way of the distance value being reduced by a specific factor and by way of a plurality of movement increments with maximum increment size being performed in accordance with this reduced distance value, which results in a position, which corresponds to the reduced distance value, being reached or approached. Reducing the distance value by a specific factor in turn ensures that the desired position is not overshot.

"If the distance value is below the second threshold value, a second phase of the approaching movement can occur, in each case by way of a movement increment with maximum increment size being performed until the first threshold value is reached.

"The real behavior, or non-ideal behavior, of the manipulator or of the actuators can be taken into account by the actually traveled section of the previous movement increment and/or the pre-specified increment size of the previous movement increment being used as the input variables for determining the increment size of the next movement increment. In this manner it is possible to take into account the actual and under certain circumstances different conditions for various actuators in the method, which results in an improved positioning accuracy and effectiveness of the positioning method."

For the URL and additional information on this patent, see: Aubele, Karl-Eugen; Merz, Erich; Rassel, Thorsten. Positioning Method for an Optical Arrangement of a Projection Illumination System. U.S. Patent Number 8810934, filed March 17, 2011, and published online on August 19, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8810934.PN.&OS=PN/8810934RS=PN/8810934

Keywords for this news article include: Carl Zeiss SMT GmbH.

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Source: Journal of Engineering


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