The invention relates to a system for inspecting and/or processing a sample on a stage with a probe or imaging apparatus.
High resolution lithography and micro-machining tools (e.g. E-beam lithography system, DUV-stepper), inspection and process-control equipment (e.g. CD-SEM, defect location and defect review tools) and analytical and test equipment (SEM, FIB, AFM, high resolution tools using UV, DUV, and EUV light sources) require stages for carrying and moving the sample to be inspected and/or processed.
With increasing resolution requirements of those systems, the demands on these stages with respect to stability and position accuracy are steadily increasing. Accuracy and stability requirements are below 100 nanometer and will probably go down below 1 nanometer. The mechanical design and mechanics of the stage no longer can fulfill the challenging demand alone. Therefore, it is necessary to apply position control means to support the stage position accuracy and stage stability.
Stage position control is performed mainly by two tools, by a linear optical encoder and by a laser-interferometer. A linear encoder consists of optical grids or gratings which are connected to the stage and whose motion is read by suitable optical sensors, which are placed on the non-moveable part of the stage setup. The laser-interferometer control uses the interference between a reflected beam, which is generated by a mirror connected with the stage, and a reference beam. Since the wavelength of the laser beam is used as a measurement unit, laser interferometers offer a much better position accuracy (in the range of 10 nm) than optical encoders which have an accuracy in the range of 100 nm.
Linear encoders have the drawback that their accuracy is limited. Laser-interferometers are much more accurate, but they are very complex and expensive. The accuracy is limited by changes in the refractive index of the optical light path and the quality of the mirrors. Furthermore, laser-interferometers are used preferably for x-y-coordinate measurements. Setups for a 3-dimensional coordinate measurement of stage position is very difficult to realize.
From EP-A-0 559 402 and U.S. Pat. No. 3,936,716 stabilization systems are known for stabilizing a platform with gyroscopic means.
It is an object of the invention to provide a system for inspecting and/or processing a sample on a stage with a probe or imaging apparatus with a precise, simple and cost-effective position control means.
It is a further object of the invention to provide means which allows both the accurate control of the position of the stage relatively to the probe or imaging apparatus and the mechanical detection and stabilization of mechanical disturbances (e.g. vibrations, drift).
The position control means can be preferably used in probe systems (particle beam systems, atomic force microscopes, high resolution tools).
The gyroscopic means is adapted to measure movements in one, two or three dimensions.
In a preferred embodiment, there is at least one motor for moving the stage and/or the probe or imaging apparatus which is operatively connected with the position control means.
The system for inspecting and/or processing a sample according to a preferred embodiment comprises a probe or imaging apparatus. The probe and/or imaging apparatus according to the disclosed embodiment is defined by a scanning probe or a column with beam generating means and means to deflect the beam. In case of a column, the column is equipped with column gyroscopic means to detect movements of the optical column. Furthermore, the control means is operatively connected with the deflection means in order to compensate uncontrolled movements (vibrations, drift) of the stage relatively to the column.
In another system for inspecting and/or processing a sample, the probe or imaging apparatus is defined by an optical column having beam generating means, means to deflect the beam and image generating means wherein the control means is operatively connected with the image generating means in which the unintentional movements of stage relative to the column will be taken into account when processing the image.