Electricity: electrical systems and devices – Electric charge generating or conducting means – Use of forces of electric charge or field
Reexamination Certificate
2000-09-19
2002-07-30
Jackson, Stephen W. (Department: 2836)
Electricity: electrical systems and devices
Electric charge generating or conducting means
Use of forces of electric charge or field
C361S115000
Reexamination Certificate
active
06426860
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This invention claims priority of a German filed patent application DE P 198 53 588.0.
FIELD OF THE INVENTION
This invention relates to a device to hold a substrate inside an exposure system in which the substrate is seated on a table traveling in the X, Y coordinates and where, between table surface and substrate, metering means for adjusting the distance and for aligning the substrate in relation to an exposure optics are provided, from where a particle radiation is directed rectangular to the substrate surface, corresponding to the Z coordinate.
BACKGROUND OF THE INVENTION
Holding devices for mounting substrates, especially for masks and wafers during exposure in optical, as well as in electro-optical exposure systems, are known to exist in different versions in the state of the art. As a rule, holding systems are arranged on a table movable in two coordinates X, Y, and have a supporting plane for the substrate on which it is seated and held prior to the exposure process while the table will be gradually moved parallel to X and/or Y, thus being adjusted to the requested exposure positions in succession. The bearing planes are mostly formed by high plane bearing surfaces, and also partially by multiple point-shaped bearing elements.
The basic bodies, mounting plates etc, on which the bearing elements are arranged or bearing surfaces are formed, are normally mechanically fixed to the table, using metering means to adjust the substrate in the Z coordinate. In this context the Z coordinate corresponds to the radiation direction of the exposure ray path and is directed rectangular to the substrate surface.
The positioning accuracy of the substrate surface, the adjustment of the bearing plane, the flatness of a bearing plane and last but not least the stability of shape of all parts and assemblies of the holding system are of essential importance for the quality and fineness gaining the structure demanded during exposure. This is the more important the more the industry of microelectronics aims at further reducing the width of structure.
For this reason an appropriate design of the holding systems have to secure accuracy in respect to dimensional and shape stability even under the influence of changes in temperature and pressure during the process of exposure. Another factor to be paid attention to with regard to the design of holding systems is, that the exposure radiation will not be affected by magnetic fields originating from magnetic components or from materials containing magnetic particles. Additionally the exposure radiation must not be deviated unintentionally by electrical chargings of the holding system. Moreover, mechanical forces, no matter of what origin, must not influence the substrate via parts or assemblies, which could cause deformations and thus inaccuracies. Besides, the costs for producing the holding device have to be kept in economically reasonable limits.
The holding systems available so far in the state of the art have to be evaluated under this very aspect of these high requirements. For example, a device for holding substrates is known from the U.S. Pat. No. 5,535,090 as well as from the publication “Semiconducter International”, Sherman, Volume 20, No. 8, p. 319-322, having an electrostatic Chuck arrangement. Chuck arrangements have electrically conductive layers to which, through supply contacts, disconnectable electrical potentials can be applied in relation to the substrates. The application generates an electrostatic field by which the substrate is kept electrostatically on an even insulation layer placed above the conductive layer. In this context the amount of the force of attraction between the Chuck arrangement and the substrate depends on the electrical voltage fed, the area size of the conductive layer (the so-called Chuck electrode) and the thickness of the insulation layer between the conductive layer and substrate.
In case of the arrangement mentioned above, sapphire is provided to be the bearing material for the substrate. Here the whole 8″ inch bearing surface was not covered by sapphire but through an intermediate layer made of niobium, only several 2 inch sapphire discs are provided which form the bearing surface for the substrate. The lavish manufacturing process of the bearing surface consisting of multiple sapphire areas is disadvantageous in this context, which, in addition to the expensive sapphire material itself, causes high cost.
The U.S. Pat. No. 5,600,530 describes another holding device for substrates, which again is equipped with an electrostatic Chuck arrangement. But here aluminum oxide is used as material for the insulation layer. At the same time a procedure is mentioned by which the aluminum oxide layer is brought to the necessary thickness for positioning the substrate by thinning down.
The use of aluminum oxide implies disadvantageous problems caused by an unfavorable temperature expansion coefficient. For this reason the use of aluminum oxide inevitably requires measures to compensate this disadvantage and to prevent changes in position and/or shape of the substrate exceeding a permissible measure. The solution to this problem, however, is not given in the paper mentioned.
Another essential disadvantage of the known state of the art is that holding systems for substrates are always only designed for substrates of a given size. For the exposure of individual substrates or series of substrates of different seizes the known holding systems can be used to a certain extent only or not at all, unless under the condition of a high expenditure of assembly and adjustment.
Another holding device for substrates for processing in an electron-beam facility is revealed in U.S. Pat. No. 5,644,137. This arrangement is equipped with interferometers to determine and monitor the position of the table and the substrate when moving the X and Y coordinates. In this case, a stabilization of the position of the substrate in relation to the exposure optics is reached insofar as some parts of the holding device and the interferometers are made of material having the same expansion behavior, resulting in a higher degree of positioning precision in the X and Y directions. This publication, however, does not show how the problems, with regard to the expansion in the Z coordinate and the thus related inaccuracies, can be solved.
SUMMARY OF THE INVENTION
Taking this into consideration the invention is intended for further improvement of a holding device of the kind, described above in such a way that bearing elements for the substrate are interchangeable with each other in a quick and uncomplicated manner with yet reaching a high degree of positioning precision.
According to the invention this task is solved by two mounting plates adjusted on the table parallel to the X, Y plane, being also directed to the exposure optics and in various distances to the table surface. The first one of the mounting plates is being connected directly to the table, the second mounting plate being in connection with the first mounting plate through at least one holding device, the holding function of which can be switched on and off, with a mounting plane for substrates being designed on that side turned to the exposure optics.
This implies the advantage that the second mounting plate provided with the bearing plane for the substrate can be detached from the first mounting plate after switching off the holding function, enabling in an easy and uncomplicated way an exchange among mounting plates with bearing planes for substrates having different sizes. Due to the parallel alignment of both mounting plates to each other and the design of reference surfaces at both mounting plates and the holding devices, an exact exposure position for the substrate is secured after every exchange.
The preferred designs of the invention provide that the first mounting plate is connected to the table through anti-vibration elements, and that the switchable holding devices, designed to hold the second mounting plate to the first, are also d
Guyenot Volker
Harnisch Gerd
Kalkowski Gerhard
Kirschstein Ulf-Carsten
Risse Stefan
Jackson Stephen W.
Leica Microsystems Lithography GmbH
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