The present invention relates to a lithography mask configuration, in particular for EUV lithography, which is used in the production of semiconductor components.
A mask that complies with very stringent requirements relating to the production tolerances is required in order to use extreme ultraviolet (EUV) lithography for the production of semiconductor components. In this type of lithography, light is not passed through the mask, rather the mask is illuminated from the side of the sample that is to be processed lithographically. The light is reflected, or is not reflected, in a manner corresponding to the structured surface of the mask. The specifications for such masks must therefore be complied with very accurately. In the case of a mask area in the order of magnitude of square centimeters, the vertical discrepancy from the plane of the surface must not exceed 100 nm. Furthermore, it is necessary to ensure that the mask can be aligned very accurately with respect to the object to be processed, during the lithography process. Thus, until now, masks composed of thick substrates with low thermal coefficients of expansion have been used, produced from a material such as Zerodur or an ultra-low-expansion glass. Owing to the large mass of these substrates, the mask is bent downward in the center due to the force of gravity when it is aligned horizontally. The bending of the mask cannot be avoided completely even when using very robust substrates. The deformation of the mask leads to lithography inaccuracies that are no longer tolerable.
It is accordingly an object of the invention to provide a lithography mask configuration which overcomes the above-mentioned disadvantages of the prior art methods of this general type, which complies with the stringent requirements needed for by EUV lithography.
With the foregoing and other objects in view there is provided, in accordance with the invention, a lithography mask configuration. The configuration includes a reflective membrane mask composed at least partially of an electrically conductive material; an electrode plate disposed over the reflective membrane mask and has a number of electrodes electrically isolated from one another and able to be electrically connected individually; and a device for applying a respective electrical potential difference between each of the electrodes individually and the reflective membrane mask. According to the invention, a configuration containing the reflective membrane mask and the electrode plate is used as the mask. The reflective mask is in the form of the membrane mask, in which the actual mask is formed by a membrane fitted in a frame. The membrane is produced at least partially from an electrically conductive material. In the simplest case, the entire membrane is an electrically conductive material, for example a conductive sheet or a thin electrically conductive polysilicon layer.
The membrane mask is aligned horizontally above a sample to be processed. The membrane of the mask thus bends downwards owing to its natural weight, so that the distance to the object disposed underneath it is reduced in the central area. This is compensated for in the configuration according to the invention by disposing an electrode plate above the membrane mask and parallel to it, which electrode plate is provided with a number of electrodes, which are electrically isolated from one another and can be electrically connected individually. Electrostatic forces are produced via suitable devices for applying a respective electrical potential difference between each individual one of the electrodes and the membrane mask, and the electrostatic forces have a locally restricted effect in an area surrounding each individual electrode. It is thus possible to correct the deformation of the membrane mask by application of suitable potentials to such an extent that the required tolerances are met.
In accordance with an added feature of the invention, a monitoring device is provided for monitoring a physical shape of the reflective membrane mask. The monitoring device includes a light source for projecting light onto the reflective membrane mask and a light detector for detecting the light reflected by the reflective membrane mask.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a lithography mask configuration, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.